Studies of autocatalytic electrocoagulation reactor for lead removal from simulated wastewater

Studies of autocatalytic electrocoagulation reactor for lead removal from simulated wastewater

Accepted Manuscript Title: Studies of Autocatalytic Electrocoagulation Reactor for Lead Removal from Simulated Wastewater Author: Forat Yasir AlJaberi...

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Accepted Manuscript Title: Studies of Autocatalytic Electrocoagulation Reactor for Lead Removal from Simulated Wastewater Author: Forat Yasir AlJaberi PII: DOI: Reference:

S2213-3437(18)30565-7 https://doi.org/10.1016/j.jece.2018.09.032 JECE 2653

To appear in: Received date: Revised date: Accepted date:

18-6-2018 11-8-2018 18-9-2018

Please cite this article as: AlJaberi FY, Studies of Autocatalytic Electrocoagulation Reactor for Lead Removal from Simulated Wastewater, Journal of Environmental Chemical Engineering (2018), https://doi.org/10.1016/j.jece.2018.09.032 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Studies of Autocatalytic Electrocoagulation Reactor for Lead Removal from Simulated Wastewater Forat Yasir AlJaberi Chemical Engineering Department, College of Engineering, University of Al Muthanna, Iraq ([email protected])

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ABSTRACT

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The removal of heavy metals from wastewater using efficient methods has caught the attention of scientists in recent years. One of these methods is the electrocoagulation technique which is widely studied and employed around the world. The aim of the present work was the study of the autocatalytic behavior of an electrocoagulation reactor that consisted of triple aluminum tubes which were constructed in a concentric manner, putting cathode electrode in between the tubes of the anode electrode. The operational parameters were the electrolysis time (2-30) min., initial lead concentration (10-300) ppm, electric current (0.2-2.6)Amps., and the mixing speed of the neutral solution was 150rpm. Results show that electrocoagulation reactor seems to be an autocatalytic reactor which improved the kinetics of the adsorption process to remove lead from the polluted solution.

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1. Introduction

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Keywords: Electrocoagulation; Autocatalytic reaction; Heavy metals; Simulated wastewater

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Several sources of wastewater containing heavy metals, such as Cu, Ni, Hg, Zn, As, Cd, Pb, and Cr that are included in industrial effluents as shown their distribution in Table 1 [1], are consistently discharged into the aquatic environment as a result of the continuous demand of heavy metals and their components in numerous industries, which causes serious problems for the environmental and health [2,3].

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Table 1 Toxic heavy metals in industrial wastewaters [1] Heavy metals Manufacturing Industries Copper Electrical, plating, rayon Nickel Electroplating, iron, steel Mercury Chlor-alkali, chemical, scientific instruments Zinc Plating, Galvanizing, iron, steel Arsenic Phosphate fertilizer, metal hardening, paints and textile Cadmium Electroplating, phosphate fertilizer, pigments Lead Battery, paints Chromium Metal plating , tanning, rubber, photographic

Heavy metal pollution has become a worldwide threat, therefore substantial trends of efficient techniques should be used to remove toxic metals from the contaminant

Table 2 Concentration limits of toxic metals in the discharged wastewater [6,7]. Toxic metals MCL (ppm) Arsenic 0.050 Mercury 0.00003 Cadmium 0.010 Lead 0.0060 Chromium 0.050

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Table 3 Regulatory limits of toxic metals in water of some [5,8]. Toxic metals EPA OSHA Arsenic 0.01 ppm 10 microg/m3 3 Mercury 0.02 microg/m 0.05-0.1 millig/m3 3 Cadmium 5.00 microg/m 5 microg/m3 Lead 0.15 microg/m3 Chromium 0.15 microg/m3 -

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wastewater before discharging it to the aquatic systems that should be according to the standards of Environmental Protection Agency (EPA-2009), Occupational Safety and Health Administration (OSHA-2009), and World Health Organization (WHO2003) [4,5] (Tables 2 and 3).

WHO 0.010 ppm 0.006 ppm 0.003 ppm 0.010 ppm 0.050 ppm

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Several methods are used to remove heavy metals from wastewaters such as chemical precipitation which depends on the change in form of the ionic constituents of pollutants dissolved in wastewater into solid particles by the addition of counterions to reduce the solubility [9]. Membrane filtration which consists of several types depending on to the size of particle that must be retained [10,11] such as Microfiltration (MIF) which is used in microorganisms removal from water, Ultrafiltration (UF) that has a higher selectivity due to the use of selective binding [11-13] but the important threat is the generation of sludge [14], Nano-filtration (NF) which is employed for the elimination of toxic metal from wastewater [15], Reverse osmosis (RO) which uses high pressure to force a solution through the membrane and depends on several parameters such as the solute concentration, pressure supplied, and the rate of water flux [16], and Electrodialysis (ED) that is classified into two types according to the polyelectrolyte membrane is inserted between anode and cathode electrodes, cation exchange and anion exchange [17-19]. Electrodialysis has a higher efficiency than RO method but the main drawback affects its performance is the voltage applied [11]. Membrane filtration types are utilizing with a high efficiency, easy operation, and space saving [12] and they could be run as pressure driven, concentration gradients, or electrical potential gradients [15]. Adsorption process which depends on the mass transfer of ions from the liquid phase to the surface of the solid phase bounded by physical and/or chemical interactions [6,7], and electrochemical techniques which are more reliable and economical when compared to other conventional techniques [20] due to its capability to make several contributions to ecological treatment, recycling, and monitoring [21,22] such as the

electroflocculation that used to separate solid/liquid by the floatation of the contaminants to the surface of wastewater depending on gases bubbles released at electrodes via the electrolysis process of wastewater [13, 23]. The main advantages and drawbacks of the previous treatment techniques are summarized in Table 4 [24].

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Table 4 The main advantages and disadvantages of the conventional treatment techniques [24] Treatment method Advantages Drawbacks Chemical  Capital cost is low  Additional cost required to precipitation disposal the huge sludge  Not complex operation  Easy operating conditions  Applicable for wide range of the pH

 Low selectivity  Generation of waste products

Membrane filtration (All types)

 Space requirement is not large  High selectivity

 High operating cost due to membrane fouling

Electroflocculation

 Captures coagulated pollutants and floats them to the surface

 Larger amount of sludge generated

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Adsorption

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Electrocoagulation process is an electrochemical technique that has an efficient ability to remove various kinds of pollutants from wastewaters such as toxic metal ions, organics, and inorganics [22, 26]. This technique depends on the creation of adsorbents due to the redox reactions via the electrocoagulation reactor as a result of the continuous flow of direct current to the electrodes. Therefore, the electrocoagulation method could be considered as an autocoagulating or electro-catalytic method without any addendum of chemicals which produces less amount of sludge compared to other conventional techniques [27]. Electrocoagulation reactor is the main part of this technique that must be well designed in order to be applicable to remove contaminants from wastewater with high efficiency [28]. Reactor design consists of two conducting electrodes that are immersed in a container filled with an electricity-conducting liquid called the electrolyte. When the current is applied to the electrodes, the cell runs and the reaction rate will be controlled depending on the polarity of these electronic electrodes [29]. Electrocoagulation reactor depends on several conditions such as the mode of operation which is batch or continuous where each one of these two modes will restrict the design, configuration, and arrangement of electrodes in order to enhance the ability of this process. In general, the electrode is the heart of this reactor and may be varied from single microelectrode to large parallel plate cell houses. The electrode may be made of plane metal such as iron, aluminium, stainless steel, or could be porous and made of the same metal for both electrodes or a combination of different electrodes metal [1]. Its configuration affects the performance of electrocoagulation reactor [29] where it could be a plane or a mesh rectangular shape. This configuration gives an active area that is

𝒅𝑪𝒕 𝒅𝒕

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restricted by the type of electrodes arrangement. This electrode arrangement could be monopolar or bipolar and the active area ranges from 0.01 m2 to 10000 m2 [29,30]. The ratio of the active area to the volume of the pre-treated wastewater (S/V) ranges from 6.9 to 42.5 m2/m3 [31]. The inter-electrode distance (gap) between plane electrodes could slow down the process of flocculation or obstruct the motion of solid and liquid materials due to the variation of the electrostatic attraction between different ions when the gap between both electrodes is enlarged or enclosed [1]. In order to represent the removal rate of a heavy metal concentration from the simulated wastewater, a general kinetic rate equation is used (Eq. (1)) [32]. = −𝑘𝐶𝑡𝑛

(1)

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where C represents the pollutant concentration, n is the order of reaction, k is the reaction rate constant, and t is the electrolysis time.

𝑑𝑡

= 𝑘𝐶𝐴 𝐶𝐶 = 𝑘𝐶𝐴 (𝐶𝑜 − 𝐶𝐴𝑜 )

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where:

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𝑑𝐶𝐴

−𝑟𝐴 = −

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The reaction occurred in the electrocoagulation reactor can be assumed as an autocatalytic reaction that depends on the production of coagulants which acts as a catalyst. The rate of reaction equation of an autocatalytic reactor could be presented as follows [32]:

(3)

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Co=(CAo+CRo)

(2)

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rA: rate of reaction (g/L.min). k : reaction rate constant (L/g.min). CA : concentration of lead (g/L). CC : concentration of aluminum hydroxide formed (g/L). CAo: initial concentration of lead (g/L). CRo: initial concentration of aluminum hydroxide formed (g/L). When (Eq. (2)) is arranged, the constant of the reaction, i.e. k, is estimated as shown in (Eq. (4)): 𝐶

(𝐶𝑜 −𝐶𝐴 )

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𝑘 = [𝑙𝑛 𝐶𝐴𝑜(𝐶 𝐴

] /[(𝐶𝐴𝑜 + 𝐶𝑅𝑜 )𝑡]

𝑜 −𝐶𝐴𝑜 )

(4)

In general, the rate of an autocatalytic reaction starts low then be rapidly increase when the concentration of reactant is high, and then drops gradually as reactant is consumed [32-36]. The present study employed a novel electrocoagulation reactor that was innovated by (AlJaberi, F.Y. and Mohammed, W.T.) [37] in order to study the autocatalytic behavior in this reactor using aluminum tubes as concentric electrodes. Where the

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continuous release of aluminum ions and hydroxyl ions tend to form different hydroxo-complexes including monomers and polymers such as Al(OH)+2, Al(OH)2+, Al2(OH)2+4, Al6(OH)15+3, Al7(OH)17+4, Al8(OH)20+7, Al13O4(OH)24+7, and Al13(OH)34+5 [38, 39]. Therefore, aluminium hydroxyl acts as an efficient adsorbent which have the ability to adsorb toxic metals from wastewater. The analysis of an electrocoagulation reactor is not simple field due to the complication in its operation along the duration of the treatment [40]. In one hand, its work depends completely on the electric current supplied which caused to release different ions at/from the electrodes. While in the other hand, the adsorption phenomena occurs depending on the interaction between the adsorbent formed and the pollutant presented in the wastewater.

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2. Experimental works

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The concentration of coagulants, i.e. catalyst, that formed along the duration of reaction due to the dissolution of aluminum electrodes was estimated using experimental analysis via a central composite design. Statistica-17 software was employed to find a mathematical correlation that relates the value of electrodes consumption to the operational variables using (Eq. (5)) according to ranges listed in Table 5.

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(5)

Ranges 2-30 10-300 2-12 0.2-2.6 0-300

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Table 5 Operational parameters Parameters X1: Contact time (min) X2: Initial lead concentration (ppm) X3: pH X4: Current (Amps.) X5: Stirring speed (rpm)

i

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Y  B0   Bi X i   Bii X i2   Bij X i X j  

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2.1.Chemicals

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Samples of simulated wastewater were prepared according to the designed experiments by dissolving the required amount of an initial concentration of nitrate salt of lead (Pb(NO3)2) provided by B.D.H (England) in distillate water. The value of acidity was adjusted using either hydrochloric acid (0.1 N) or sodium hydroxide ( 0.1 N), as required. In order to prevent electrodes passivation and to enhance the conductivity of the simulated samples, 100ppm of sodium chloride provided by Merck (Germany) was used. 2.2. Instruments Amounts of lead nitrate and sodium chloride were weighed using a digital balance (500g x 0.01g) manufactured by PROF company (China) while solution pH was measured using pH meter supplied by ATC company (China).

2.3.

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Digital DC- power supply that was manufactured by SYADGONG company (China), model 305D, 0-30 volt and 0-5 Amps., was employed to supply current to the electrodes immersed in the simulated wastewater. Collected samples from the treated solution were filtered using cellulose Glass-Microfibre discs (Grade: MGC; pore diameter is 0.47 micrometre) provided by MUNKTELL (Sweden). Values of lead concentration presented in samples of the treated wastewater were measured using Atomic Absorption Spectroscopy (AAS- 7000F) manufactured by SHIMADZUAA (Japan).

Apparatus

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The electrocoagulation reactor was made up of 1L cylindrical PVC beaker, with a wooden and PVC cover supporting the set of monopolar-parallel concentric electrodes where a small drilled hole was situated in the cover to serve as a sampling port. The elemental composition of the aluminum electrodes was investigated by the Energy Dispersive Spectrometric EDS test using (Oxford instrument-X-act) that was manufactured by (United Kingdom) and X-ray test using (X-Ray Diffractometer XRD 6000 / Shimadzu-Japan) as reported in Table 6 and Fig. 1.

O 3.82

C 12.33

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Table 6 The elemental composition of aluminum tubes as weight percentage. Metal Al Mg Fe Si Weight % 82.06 0.97 0.06 0.76

Fig. 1. Elemental composition of aluminum tube (EDS-test)

Table 7 illustrates the dimensions of the concentric electrodes that are made of aluminum tubes where these dimensions involved the height of tubes, wet height, outer and inner diameters, the distance in between the tubes, and the thicknesses of these tubes individually.

Table 7 Dimensions of the aluminum tubes. Tube height Tube wet (cm) height (cm) Outer tube

9.70

4.00

Tube thick. (cm) 0.20

Outer diameter (cm) 7.70

Inner diameter (cm) 7.30

Distance in between (cm) 1.60

Mid. tube

8.50

4.00

0.15

5.85

5.55

1.55

Inner tube

7.10

4.00

0.30

4.30

3.70

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Fig. 2 shows the schematic of electrocoagulation reactor and electrodes configuration used in the present study.

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Fig. 2. Schematic of the electrocoagulation reactor and electrodes configuration

3. Results and discussion

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Coagulants generation and bubble formation are the main issues that should be presented in any design characteristics of the electrocoagulation reactor. Therefore, the present work focused on the formation of coagulants used as a catalyst in the innovated reactor. 3.1. Concentrations of coagulants

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According to the central composite design of experiments, thirty-two experiments were employed to evaluate a mathematical correlation that related the concentration of coagulants formed to the operating parameters. The dissolution of electrodes occurred due to the continuous charge of direct current from DC-power supply to the electrodes when they immersed in the contaminated solution. The catalyst formed as a result of that consumption of electrodes when different ions of aluminum and hydroxyl are released at both electrodes and reacted together along the duration of the experiment and varied in their amounts belong to the values of the operating variables.

According to (Eq. (5)), the mathematical correlation that relates the amount of catalyst generated to the operational variables as listed their ranges in Table 5, is shown in (Eq. (6)) as follows: Concentration of catalyst formed (R2= 0.950):

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CR = - 0.025 - 0.00774 X1 + 0.00107 X2+ 0.0541 X3 – 0.090 X4 - 0.000867 X5 + 0.000101 X12 + 0.000002 X22 - 0.00275 X32 +0.0264 X42 + 0.000004 X52 0.000011 X1 X2+ 0.001291 X1 X3 + 0.00336 X1 X4 - 0.000021 X1 X5 0.000183 X2 X3 + 0.000155 X2 X4 - 0.000001 X2 X5 - 0.0120 X3 X4 0.000043 X3 X5 + 0.000417 X4 X5 (6)

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The present work chose double of aluminum tubes to be as the anode which caused to release more of aluminum ions due to the dissolution operation then the amount of catalyst increased. While, the location of cathode in between caused to increase the formation of catalyst in rapid case due to the generation of gases bubbles, i.e. H2 and O2, in both sides that may minimized by the formation of the oxide layer on the cathode. The formation of oxide layer, i.e. electrode passivation, caused to minimize the active area of the cathode which is required to accomplish the generation of catalyst depending on the hydroxyl ion released. Therefore, this layer must be removed by changing the polarity of the electrodes, the mechanical cleaning of these electrodes, or by adding electrolyte as done in the present study. Sodium chloride used as inhibitor to prevent the formation of the oxide layer as done by [41,42]. The irregular behavior of the generation of catalyst was occurred along the duration of electrocoagulation process due to the uncontrolled processes of the formation and removing of the oxide layer on the cathode.

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3.2. Concentrations of lead

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Other experiments were employed in the same reactor to find the concentration of lead presented in the treated solution when the operating variables were taken as designed in Table 5 but the value of the electrolysis time was (2, 5, 10, 15, 20, 25, and 30)min as well as the values of pH and the agitation speed were taken as 7 and 150rpm respectively. Samples of the treated wastewater were collected at each value of the designed time and filtrated then using Atomic Absorption Spectroscopy (AAS) to estimate the concentration of lead presented in these samples as shown their values in Tables 8 to 14. The removal of lead from the wastewater in such type of electrochemical reactors occurs in three ways [39]; the electrodeposition on the cathode, the formation of lead hydroxides then settled as a sludge, and the adsorption process of the pollutant on the aluminum hydroxides. As shown in the results, the higher removal of lead obtained the higher values of electric supplied. The final concentration of lead equals or little more than the

specifications in the mentioned tables without any formation of second pollution as presented in the chemical precipitation. But, in general, the present work focuses on the autocatalytic behavior in such kind of electrochemical reactors. Moreover, Tables 8 to 14 explain the values of catalyst concentration formed in the electrocoagulation reactor according to the model presented by (Eq. (6)) for the range of 2min up to the saturation status occurred at time 30min, neutral solution samples, 150rpm of mixing speed and several values of electric current applied for each value of the initial lead concentration presented in wastewater.

2.2 Amps.

C Ro

CA

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4.547 3.948 3.058 2.302 1.681 1.193 0.839

0.170 0.178 0.297 0.437 0.597 0.777 0.978

3.030 2.509 1.747 1.119 0.625 0.266 0.040

0.179 0.198 0.344 0.511 0.698 0.905 1.132

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2.6 Amps.

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1.8 Amps.

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Table 8 Concentrations of lead and catalyst (Initial lead concentration: 10ppm; pH=7; mixing speed: 150rpm). Contact 0.2 Amps. 0.6 Amps. 1.0 Amps. 1.4 Amps. Time CA C Ro CA C Ro CA C Ro CA C Ro (min.) 2 9.449 0.659 8.398 0.458 7.231 0.309 5.947 0.213 5 8.543 0.632 7.569 0.438 6.479 0.296 5.272 0.207 10 7.140 0.594 6.294 0.411 5.332 0.305 4.254 0.284 15 5.871 0.566 5.154 0.418 4.320 0.391 3.369 0.397 20 4.737 0.546 4.147 0.498 3.442 0.497 2.619 0.530 25 3.736 0.605 3.275 0.597 2.697 0.623 2.003 0.683 30 2.869 0.697 2.536 0.717 2.087 0.770 1.521 0.857

CA

C Ro

2.272 1.828 1.194 0.695 0.329 0.098 0.001

0.241 0.255 0.425 0.618 0.832 1.066 1.320

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Table 9 Concentrations of lead and catalyst (Initial lead concentration: 50ppm; pH=7; mixing speed: 150rpm). Contact 0.2 Amps. 0.6 Amps. 1.0 Amps. 1.4 Amps. Time CA C Ro CA C Ro CA C Ro CA C Ro (min.) 2 43.050 0.576 38.384 0.380 33.135 0.238 27.304 0.148 5 38.549 0.552 34.267 0.364 29.404 0.228 23.957 0.174 10 31.584 0.520 27.943 0.343 23.721 0.269 18.915 0.258 15 25.289 0.497 22.289 0.363 18.708 0.345 14.543 0.361 20 19.664 0.483 17.306 0.433 14.365 0.442 10.842 0.485 25 14.710 0.521 12.992 0.523 10.693 0.559 7.810 0.629 30 10.426 0.604 9.349 0.634 7.691 0.697 5.449 0.794 Contact Time (min.) 2 5 10 15 20 25 30

1.8 Amps.

2.2 Amps.

2.6 Amps.

CA

C Ro

CA

C Ro

CA

C Ro

20.891 17.929 13.528 9.797 6.736 4.346 2.626

0.114 0.170 0.281 0.411 0.562 0.733 0.924

14.681 12.103 8.343 5.253 2.833 1.084 0.005

0.128 0.200 0.338 0.495 0.673 0.871 1.089

11.088 8.894 5.775 3.326 1.548 0.439 0.001

0.194 0.264 0.428 0.613 0.817 1.042 1.287

1.8 Amps.

2.2 Amps.

2.6 Amps.

C Ro

CA

C Ro

CA

C Ro

38.286 32.435 23.755 16.416 10.417 5.759 2.441

0.139 0.188 0.287 0.406 0.546 0.705 0.885

28.715 23.633 16.235 10.178 5.461 2.085 0.049

0.165 0.231 0.357 0.503 0.669 0.855 1.062

21.529 17.216 11.101 6.325 2.891 0.796 0.043

0.225 0.307 0.460 0.632 0.826 1.039 1.272

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Table 10 Concentrations of lead and catalyst (Initial lead concentration: 100ppm; pH=7; mixing speed: 150rpm). Contact 0.2 Amps. 0.6 Amps. 1.0 Amps. 1.4 Amps. Time CA C Ro CA C Ro CA C Ro CA C Ro (min.) 2 76.723 0.489 68.861 0.302 59.834 0.188 49.643 0.146 5 67.795 0.470 60.702 0.289 52.445 0.205 43.022 0.180 10 53.987 0.445 48.177 0.282 41.201 0.250 33.061 0.252 15 41.520 0.429 36.991 0.321 31.298 0.315 24.439 0.344 20 30.393 0.422 27.147 0.379 22.735 0.401 17.159 0.456 25 20.607 0.443 18.642 0.458 15.513 0.506 11.218 0.589 30 12.161 0.515 11.479 0.557 9.631 0.632 6.619 0.742

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Table 11 Concentrations of lead and catalyst (Initial lead concentration: 150ppm; pH=7; mixing speed: 150rpm). Contact 0.2 Amps. 0.6 Amps. 1.0 Amps. 1.4 Amps. Time CA C Ro CA C Ro CA C Ro CA C Ro (min.) 2 102.873 0.423 93.285 0.281 81.950 0.218 68.868 0.189 5 89.591 0.408 81.157 0.275 70.976 0.228 59.047 0.215 10 69.064 0.390 62.552 0.281 54.294 0.262 44.288 0.276 15 50.546 0.381 45.958 0.308 39.623 0.316 31.540 0.357 20 34.040 0.381 31.375 0.355 26.963 0.389 20.803 0.457 25 19.544 0.395 18.802 0.423 16.313 0.484 12.076 0.578 30 7.060 0.456 8.240 0.510 7.674 0.598 5.360 0.720

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Contact Time (min.) 2 5 10 15 20 25 30

1.8 Amps.

2.2 Amps.

2.6 Amps.

CA

C Ro

CA

C Ro

CA

C Ro

54.038 45.371 32.536 21.710 12.896 6.092 1.300

0.194 0.236 0.324 0.431 0.559 0.707 0.875

41.976 34.463 23.551 14.648 7.757 2.876 0.007

0.232 0.291 0.405 0.540 0.695 0.870 1.065

31.212 24.853 15.863 8.884 3.916 0.958 0.011

0.305 0.380 0.521 0.682 0.864 1.066 1.288

1.8 Amps.

2.2 Amps.

2.6 Amps.

C Ro

CA

C Ro

CA

C Ro

69.999 58.590 41.721 27.532 16.025 7.198 1.053

0.279 0.314 0.390 0.486 0.603 0.739 0.896

54.636 44.766 30.461 18.836 9.893 3.630 0.049

0.330 0.382 0.484 0.607 0.751 0.914 1.098

40.244 31.913 20.171 11.111 4.731 1.033 0.015

0.414 0.483 0.612 0.762 0.932 1.123 1.333

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Table 12 Concentrations of lead and catalyst (Initial lead concentration: 200ppm; pH=7; mixing speed: 150rpm). Contact 0.2 Amps. 0.6 Amps. 1.0 Amps. 1.4 Amps. Time CA C Ro CA C Ro CA C Ro CA C Ro (min.) 2 126.412 0.412 113.508 0.328 101.335 0.278 86.832 0.261 5 108.850 0.383 97.485 0.315 86.850 0.281 73.885 0.281 10 81.725 0.355 72.923 0.311 64.852 0.303 54.451 0.330 15 57.280 0.353 51.043 0.326 45.536 0.346 37.699 0.399 20 35.517 0.360 31.843 0.361 28.900 0.408 23.627 0.488 25 16.434 0.377 15.325 0.417 14.946 0.491 12.237 0.598 30 0.033 0.426 1.487 0.493 3.672 0.594 3.527 0.728

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Table 13 Concentrations of lead and catalyst (Initial lead concentration: 250ppm; pH=7; mixing speed: 150rpm). Contact 0.2 Amps. 0.6 Amps. 1.0 Amps. 1.4 Amps. Time CA C Ro CA C Ro CA C Ro CA C Ro (min.) 2 156.263 0.477 138.383 0.406 120.366 0.368 105.387 0.364 5 134.494 0.442 118.537 0.386 102.443 0.364 89.387 0.376 10 100.894 0.398 88.142 0.370 75.253 0.375 65.402 0.414 15 70.644 0.375 61.097 0.374 51.413 0.406 44.767 0.472 20 43.746 0.372 37.404 0.398 30.925 0.457 27.484 0.549 25 20.199 0.390 17.062 0.442 13.788 0.528 13.552 0.648 30 0.004 0.427 0.072 0.506 0.002 0.619 2.971 0.766

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Contact Time (min.) 2 5 10 15 20 25 30

1.8 Amps.

2.2 Amps.

2.6 Amps.

CA

C Ro

CA

C Ro

CA

C Ro

88.021 73.944 53.164 35.734 21.656 10.929 3.554

0.393 0.422 0.487 0.571 0.676 0.801 0.946

67.743 55.589 38.014 23.789 12.916 5.394 1.223

0.457 0.502 0.593 0.705 0.836 0.988 1.160

48.678 38.447 24.077 13.057 5.389 1.072 0.106

0.554 0.615 0.734 0.872 1.031 1.209 1.408

1.8 Amps.

2.2 Amps.

2.6 Amps.

C Ro

CA

C Ro

CA

C Ro

109.957 93.285 68.716 48.168 31.642 19.137 10.654

0.538 0.560 0.613 0.686 0.780 0.893 1.027

90.034 75.669 54.946 38.244 25.564 16.905 12.268

0.614 0.652 0.732 0.832 0.952 1.093 1.253

66.616 54.559 37.682 24.826 15.992 11.179 10.388

0.724 0.778 0.885 1.012 1.159 1.326 1.514

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Contact Time (min.) 2 5 10 15 20 25 30

IP T

Table 14 Concentrations of lead and catalyst (Initial lead concentration: 300ppm; pH=7; mixing speed: 150rpm). Contact 0.2 Amps. 0.6 Amps. 1.0 Amps. 1.4 Amps. Time CA C Ro CA C Ro CA C Ro CA C Ro (min.) 2 185.458 0.572 164.062 0.513 142.381 0.488 126.387 0.496 5 159.555 0.530 140.467 0.487 121.094 0.478 107.407 0.502 10 119.602 0.475 104.360 0.459 88.833 0.477 78.992 0.528 15 83.670 0.441 72.274 0.451 60.593 0.496 54.598 0.574 20 51.760 0.426 44.210 0.464 36.375 0.535 34.226 0.640 25 23.871 0.432 20.167 0.496 16.178 0.595 17.875 0.727 30 0.004 0.458 0.146 0.549 0.003 0.675 5.546 0.834

N

3.3. Rate of autocatalytic reaction

A

CC E

PT

ED

M

A

According to equations (Eq. (2)) and (Eq. (4)) and the measured values of lead and catalyst concentration that listed in Tables 8 to14; Tables (15-21) list data of rate of reaction equations, i.e. ri and k, against the values of both lead and catalyst concentrations in case of each value of the initial concentration of lead, neutral solutions, and 150rpm of mixing speed along the time of the electrocatalytic reaction for several values of electric current applied. These data show the increase of the values of ri and k along the duration of the experiment due to the increment of releasing ions required to form the catalyst as the value of current increased, the higher current supplied the higher amount of catalyst generated, then the values of reaction equations increased.

1.8 Amps.

2.2 Amps.

2.6 Amps.

ri=10ppm

k10

ri=10ppm

k10

ri=10ppm

0.3679 0.1711 0.0940 0.0701 0.0584 0.0504 0.0432

0.2841 0.1200 0.0855 0.0705 0.0586 0.0467 0.0354

0.5705 0.2688 0.1524 0.1179 0.1012 0.0906 0.1027

0.3099 0.1332 0.0916 0.0674 0.0442 0.0218 0.0047

0.6902 0.3333 0.1883 0.1406 0.1141 0.1033 0.1818

0.3785 0.1554 0.0955 0.0604 0.0312 0.0108 0.00024

SC R

k10

N

U

Contact Time (min.) 2 5 10 15 20 25 30

IP T

Table 15 Reaction equation values (Initial lead concentration: 10ppm; pH=7; mixing speed: 150rpm). Contact 0.2 Amps. 0.6 Amps. 1.0 Amps. 1.4 Amps. Time k10 ri=10ppm k10 ri=10ppm k10 ri=10ppm k10 ri=10ppm (min.) 2 0.0049 0.0304 0.0716 0.2752 0.1457 0.3257 0.2392 0.3032 5 0.0189 0.1020 0.0431 0.1427 0.0732 0.1403 0.1144 0.1245 10 0.0205 0.0871 0.0329 0.0851 0.0485 0.0788 0.0663 0.0802 15 0.0207 0.0688 0.0294 0.0634 0.0380 0.0641 0.0500 0.0668 20 0.0216 0.0557 0.0266 0.0550 0.0329 0.0563 0.0420 0.0584 25 0.0217 0.0490 0.0252 0.0492 0.0299 0.0502 0.0371 0.0507 30 0.0219 0.0439 0.0243 0.0441 0.0276 0.0443 0.0329 0.0429

1.8 Amps.

k50

A

CC E

Contact Time (min.) 2 5 10 15 20 25 30

PT

ED

M

A

Table 16 Rate of reaction values (Initial lead concentration: 50ppm; pH=7; mixing speed: 150rpm). Contact 0.2 Amps. 0.6 Amps. 1.0 Amps. 1.4 Amps. Time k50 ri=50ppm k50 ri=50ppm k50 ri=50ppm k50 ri=50ppm (min.) 2 0.0286 0.7078 0.0441 0.6440 0.0638 0.5032 0.0917 0.3704 5 0.0155 0.3302 0.0218 0.2712 0.0304 0.2037 0.0415 0.1733 10 0.0111 0.1825 0.0147 0.1411 0.0191 0.1217 0.0250 0.1219 15 0.0101 0.1269 0.0128 0.1032 0.0158 0.1019 0.0205 0.1078 20 0.0103 0.0975 0.0122 0.0913 0.0148 0.0942 0.0194 0.1020 25 0.0111 0.0848 0.0126 0.0857 0.0151 0.0904 0.0199 0.0980 30 0.0126 0.0796 0.0139 0.0823 0.0163 0.0875 0.0215 0.0931

0.1320 0.0579 0.0352 0.0299 0.0298 0.0326 0.0370

2.2 Amps.

2.6 Amps.

ri=50ppm

k50

ri=50ppm

k50

ri=50ppm

0.3139 0.1768 0.1339 0.1206 0.1127 0.1037 0.0899

0.1899 0.0852 0.0555 0.0523 0.0607 0.0827 0.1715

0.3557 0.2066 0.1562 0.1359 0.1156 0.0781 0.0009

0.2348 0.1102 0.0748 0.0734 0.0865 0.1056 0.1795

0.5063 0.2588 0.1849 0.1495 0.1094 0.0483 0.0003

1.8 Amps.

2.2 Amps.

2.6 Amps.

ri=10ppm

k100

ri=10ppm

k100

ri=10ppm

0.0793 0.0361 0.0232 0.0211 0.0233 0.0303 0.0472

0.4215 0.2203 0.1584 0.1408 0.1322 0.1230 0.1019

0.1051 0.0486 0.0329 0.0324 0.0404 0.0645 0.1425

0.4976 0.2651 0.1905 0.1656 0.1475 0.1151 0.0075

0.1346 0.0639 0.0455 0.0479 0.0642 0.0997 0.1188

0.6515 0.3375 0.2323 0.1916 0.1532 0.0825 0.0064

SC R

k100

A

N

U

Contact Time (min.) 2 5 10 15 20 25 30

IP T

Table 17 Reaction equation values (Initial lead concentration: 100ppm; pH=7; mixing speed: 150rpm). Contact 0.2 Amps. 0.6 Amps. 1.0 Amps. 1.4 Amps. Time k100 ri=100ppm k100 ri=100ppm k100 ri=100ppm k100 ri=100ppm (min.) 2 0.0250 0.9391 0.0335 0.6967 0.0447 0.5022 0.0587 0.4262 5 0.0124 0.3947 0.0161 0.2828 0.0207 0.2225 0.0267 0.2063 10 0.0085 0.2048 0.0108 0.1463 0.0132 0.1358 0.0168 0.1395 15 0.0078 0.1391 0.0094 0.1119 0.0114 0.1121 0.0145 0.1219 20 0.0083 0.1062 0.0096 0.0983 0.0114 0.1036 0.0148 0.1156 25 0.0099 0.0900 0.0108 0.0926 0.0128 0.1004 0.0170 0.1123 30 0.0135 0.0846 0.0140 0.0897 0.0161 0.0982 0.0219 0.1075

1.8 Amps.

A

CC E

Contact Time (min.) 2 5 10 15 20 25 30

PT

ED

M

Table 18 Reaction equation values (Initial lead concentration: 150ppm; pH=7; mixing speed: 150rpm). Contact 0.2 Amps. 0.6 Amps. 1.0 Amps. 1.4 Amps. Time k150 ri=150ppm k150 ri=150ppm k150 ri=150ppm k150 ri=150ppm (min.) 2 0.0228 0.9932 0.0284 0.7425 0.0350 0.6239 0.0439 0.5708 5 0.0111 0.4061 0.0136 0.3026 0.0164 0.2660 0.0204 0.2595 10 0.0077 0.2069 0.0091 0.1608 0.0108 0.1537 0.0133 0.1631 15 0.0073 0.1403 0.0084 0.1188 0.0098 0.1222 0.0121 0.1365 20 0.0083 0.1076 0.0092 0.1021 0.0105 0.1105 0.0133 0.1263 25 0.0116 0.0899 0.0119 0.0948 0.0134 0.1056 0.0173 0.1209 30 0.0255 0.0820 0.0214 0.0901 0.0221 0.1012 0.0291 0.1122 2.2 Amps.

2.6 Amps.

k150

ri=150ppm

k150

ri=150ppm

k150

ri=150ppm

0.0572 0.0267 0.0179 0.0171 0.0204 0.0313 0.0788

0.5987 0.2865 0.1889 0.1606 0.1474 0.1347 0.0896

0.0728 0.0344 0.0240 0.0242 0.0315 0.0548 0.1777

0.7093 0.3455 0.2289 0.1918 0.1697 0.1371 0.0012

0.0946 0.0460 0.0339 0.0372 0.0537 0.0978 0.1395

0.9000 0.4336 0.2800 0.2253 0.1816 0.0999 0.0020

1.8 Amps.

2.2 Amps.

2.6 Amps.

ri=200ppm

k200

ri=200ppm

k200

ri=200ppm

0.0437 0.0207 0.0143 0.0140 0.0172 0.0280 0.0925

0.8525 0.3820 0.2322 0.1870 0.1661 0.1492 0.0872

0.0554 0.0266 0.0189 0.0195 0.0260 0.0473 0.1547

0.9974 0.4546 0.2793 0.2235 0.1931 0.1569 0.0083

0.0732 0.0361 0.0273 0.0310 0.0472 0.0962 0.1353

1.2212 0.5565 0.3377 0.2621 0.2082 0.1115 0.0027

SC R

k200

N

U

Contact Time (min.) 2 5 10 15 20 25 30

IP T

Table 19 Reaction equation values (Initial lead concentration: 200ppm; pH=7; mixing speed: 150rpm). Contact 0.2 Amps. 0.6 Amps. 1.0 Amps. 1.4 Amps. Time k200 ri=200ppm k200 ri=200ppm k200 ri=200ppm k200 ri=200ppm (min.) 2 0.0204 1.0652 0.0245 0.9119 0.0289 0.8135 0.0349 0.7907 5 0.0100 0.4181 0.0118 0.3638 0.0138 0.3363 0.0165 0.3418 10 0.0071 0.2053 0.0082 0.1860 0.0094 0.1842 0.0111 0.1997 15 0.0069 0.1404 0.0079 0.1322 0.0089 0.1395 0.0105 0.1582 20 0.0085 0.1090 0.0095 0.1098 0.0103 0.1215 0.0122 0.1409 25 0.0147 0.0913 0.0155 0.0990 0.0154 0.1127 0.0179 0.1311 30 0.4484 0.0063 0.1010 0.0740 0.0453 0.0988 0.0439 0.1126

1.8 Amps.

k250

A

CC E

Contact Time (min.) 2 5 10 15 20 25 30

PT

ED

M

A

Table 20 Reaction equation values (Initial lead concentration: 250ppm; pH=7; mixing speed: 150rpm). Contact 0.2 Amps. 0.6 Amps. 1.0 Amps. 1.4 Amps. Time k250 ri=250ppm k250 ri=250ppm k250 ri=250ppm k250 ri=250ppm (min.) 2 0.0168 1.2564 0.0202 1.1361 0.0243 1.0753 0.0283 1.0847 5 0.0083 0.4901 0.0098 0.4488 0.0117 0.4360 0.0135 0.4541 10 0.0058 0.2351 0.0069 0.2239 0.0081 0.2292 0.0093 0.2509 15 0.0058 0.1535 0.0068 0.1541 0.0080 0.1662 0.0090 0.1890 20 0.0072 0.1166 0.0083 0.1236 0.0098 0.1389 0.0107 0.1617 25 0.0124 0.0976 0.0143 0.1080 0.0171 0.1241 0.0166 0.1459 30 0.5078 0.0008 0.3586 0.0130 0.3474 0.0005 0.0515 0.1173

0.0340 0.0162 0.0112 0.0109 0.0130 0.0194 0.0412

2.2 Amps.

2.6 Amps.

ri=250ppm

k250

ri=250ppm

k250

ri=250ppm

1.1789 0.5067 0.2895 0.2222 0.1909 0.1701 0.1386

0.0439 0.0212 0.0152 0.0157 0.0205 0.0345 0.0751

1.3589 0.5929 0.3434 0.2634 0.2218 0.1842 0.1067

0.0599 0.0299 0.0231 0.0268 0.0426 0.0935 0.1155

1.6151 0.7075 0.4079 0.3055 0.2366 0.1212 0.0173

1.8 Amps.

2.2 Amps.

2.6 Amps.

ri=300ppm

k300

ri=300ppm

k300

ri=300ppm

0.0265 0.0126 0.0086 0.0081 0.0090 0.0115 0.0161

1.5712 0.6584 0.3606 0.2664 0.2222 0.1963 0.1761

0.0322 0.0153 0.0104 0.0098 0.0107 0.0124 0.0134

1.7796 0.7555 0.4200 0.3123 0.2600 0.2282 0.2061

0.0429 0.0208 0.0148 0.0145 0.0160 0.0172 0.0147

2.0681 0.8830 0.4922 0.3634 0.2973 0.2553 0.2314

SC R

k300

U

Contact Time (min.) 2 5 10 15 20 25 30

IP T

Table 21 Reaction equation values (Initial lead concentration: 300ppm; pH=7; mixing speed: 150rpm). Contact 0.2 Amps. 0.6 Amps. 1.0 Amps. 1.4 Amps. Time k300 ri=300ppm k300 ri=300ppm k300 ri=300ppm k300 ri=300ppm (min.) 2 0.0142 1.5120 0.0170 1.4273 0.0202 1.4044 0.0231 1.4474 5 0.0070 0.5894 0.0082 0.5620 0.0097 0.5637 0.0110 0.5946 10 0.0049 0.2811 0.0058 0.2767 0.0068 0.2889 0.0076 0.3166 15 0.0049 0.1810 0.0057 0.1861 0.0067 0.2026 0.0073 0.2295 20 0.0061 0.1346 0.0071 0.1449 0.0084 0.1635 0.0086 0.1895 25 0.0106 0.1096 0.0123 0.1228 0.0147 0.1416 0.0128 0.1666 30 0.4789 0.0009 0.3025 0.0242 0.3200 0.0006 0.0307 0.1418

M

A

N

In general, the rate of materials disappearing starts slowly in the autocatalytic electrocoagulation reactor because little of the catalyst is produced; it maximizes as catalyst amount is increased and then the rate drops again to a low value as reactant is consumed.

A

CC E

PT

ED

However, there are few previous studies on lead removal, especially when it is present alone in the wastewaters [27]. In general, previous studies investigated the ability of the electrocoagulation reactor to remove heavy metals using several designs of electrodes except the concentric tubes configuration as what done by the present work as well as the study of the autocatalytic behavior in such design of concentric tubes electrocoagulation reactor. Escobar, et al, 2006, used plane steel sheets for both electrodes for the treatment of simulated wastewater containing 12, 4, and 4ppm of copper, lead, and cadmium respectively [41]. Mahvi and Bazrafshan, 2007, studied the evaluation of removing cadmium from wastewater by electrocoagulation process using plane aluminum sheets as the electrodes [42]. Shakir and Husein, 2009, employed plane aluminum/steel monopolar electrodes via a batch electrocoagulation reactor to remove from wastewater [43].Wided, et al, 2014, investigated the influence of using plane aluminum electrodes to remove lead and copper from wastewater a batch electrocoagulation reactor [40].Abdul Rehman, et al, 2015, investigated the effect of plane electrode metals on the output responses by using aluminum and iron metals respectively [44].Al-Nuaimi, et al, 2016, used iron metal plane plates electrodes for chromium (VI) removal from wastewater by a batch electrocoagulation reactor [45].

SC R

IP T

Figs. 3 to 9 show that the rate of autocatalytic reaction is similar for all values of current applied to the electrochemical cell. It starts slowly, then maximizes up to the ultimate value and then tends to minimize until the end of the experiment is reached. The behavior of this reaction is uneven for all values of initial lead concentration due to the unstable redox reaction among the electrodes which leads to the difference in the amount of aluminum ions released as a result of the dissolution of electrodes as well as hydroxyl ions generated at cathode electrode. Fig. 3 compares the behavior of reaction rate when the initial lead concentration is 10ppm which suggests that the lowest value of reaction rate occurred when the current was 0.2Amps. in contrast to the reaction behavior when the current was at its maximum value. Other values of current caused the behavior of reaction to be uneven due to the irregular behavior of intermediate reaction between different ions that are released in the electrocoagulation reactor.

N

U

However, Figs. 4, 5, and 6 show different behavior of reaction curves when the initial concentration of lead was 50, 100, and 150ppm respectively. The maximum value of reaction rate achieved at the lowest value of current applied unlike the rest of other values of current that differ in their behavior according to the efficiency of lead removal from the simulated wastewater.

M

A

Figs. 7, 8 and 9 show different behavior in their reaction curves in contrast to that behavior in the previous curves. When the initial concentration of lead was maximized, the ultimate value of reaction rate was achieved at the maximum value of the current supplied to the electrochemical reactor.

0.35 0.3 0.25

PT

rA (g/L.min)

current= 0.2 Amps. current= 0.6 Amps. current= 1.0 Amps. current= 1.4 Amps. current= 1.8 Amps. current= 2.2 Amps. current= 2.6 Amps.

ED

0.4

0.2

0.15

CC E

0.1

0.05

A

0 0

5

10

15

20

25

30

35

40

Time (min.)

Fig. 3. Effect of electric current on the rate of autocatalytic reaction along the time of electrolysis (Lead concentration: 10ppm ; pH=7 ; mixing speed:150rpm)

0.8 current= 0.2 Amps. current= 0.6 Amps. current= 1.0 Amps. current= 1.4 Amps. current= 1.8 Amps. current= 2.2 Amps. current= 2.6 Amps.

0.7

rA (g/L.min)

0.6 0.5 0.4 0.3 0.2

0 0

5

10

IP T

0.1 15 20 25 30 35 40 Time (min.) Fig. 4. Effect of electric current on the rate of autocatalytic reaction along the duration of electrolysis

SC R

(Lead concentration: 50ppm; pH=7; mixing speed:150rpm) 1

current= 0.2 Amps. current= 0.6 Amps. current= 1.0 Amps. current= 1.4 Amps. current= 1.8 Amps. current= 2.2 Amps. current= 2.6 Amps.

U N

0.6 0.4

A

rA (g/L.min)

0.8

M

0.2 0 5

10

15 20 25 30 35 40 Time (min.) Fig. 5. Effect of electric current on the rate of autocatalytic reaction along the duration of electrolysis

ED

0

PT

(Lead concentration: 100ppm; pH=7; mixing speed:150rpm) 1

current= 0.2 Amps. current= 0.6 Amps. current= 1.0 Amps. current= 1.4 Amps. current= 1.8 Amps. current= 2.2 Amps. current= 2.6 Amps.

rA (g/L.min)

A

CC E

0.8 0.6 0.4 0.2 0

0

5

10

15 20 25 30 35 40 Time (min.) Fig. 6. Effect of electric current on the rate of autocatalytic reaction along the duration of electrolysis (Lead concentration: 150ppm; pH=7; mixing speed:150rpm)

1.4

current= 0.2 Amps. current= 0.6 Amps. current= 1.0 Amps. current= 1.4 Amps. current= 1.8 Amps. current= 2.2 Amps. current= 2.6 Amps.

1.2

rA (g/L.min)

1 0.8 0.6 0.4

0 0

5

10

15 20 25 Time (min.)

30

35

40

IP T

0.2

SC R

Fig. 7. Effect of electric current on the rate of autocatalytic reaction along the duration of electrolysis (Lead concentration: 200ppm; pH=7; mixing speed:150rpm) 1.8 1.4

N

1.2 1

A

0.8 0.6

M

rA (g/L.min)

current= 0.2 Amps. current= 0.6 Amps. current= 1.0 Amps. current= 1.4 Amps. current= 1.8 Amps. current= 2.2 Amps. current= 2.6 Amps.

U

1.6

0.4 0 0

ED

0.2 5

10

15 20 25 30 35 40 Time (min.) Fig. 8. Effect of electric current on the rate of autocatalytic reaction along the duration of electrolysis

PT

(Lead concentration: 250ppm; pH=7; mixing speed:150rpm)

2.2 2 1.8 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0

rA (g/L.min)

A

CC E

current= 0.2 Amps. current= 0.6 Amps. current= 1.0 Amps. current= 1.4 Amps. current= 1.8 Amps. current= 2.2 Amps. current= 2.6 Amps.

0

5

10

15 20 25 30 35 40 Time (min.) Fig. 9. Effect of electric current on the rate of autocatalytic reaction along the duration of electrolysis (Lead concentration: 300ppm; pH=7; mixing speed:150rpm)

IP T

As mentioned before, the nearest interpretation of the irregular behavior of the rate reaction curves in Figs. 3 to 9, is the formation of oxide layer above the cathode electrode that may leads to minimize the active area. Then, low releasing of hydroxyl ions, which is important to form catalyst in cooperate with aluminum ions released as a result of the dissolution of electrodes. Therefore, the autocatalytic reaction was uneven along the duration of electrolysis in case of different values of current. Since the current is the main parameter in such method of wastewater treatment, the path and behavior of reaction curves are therefore dependent on this effective parameter.

4. Conclusions

PT

References

ED

M

A

N

U

SC R

The reaction throughout the electrocoagulation process could be classified as an autocatalytic reaction due to the production of some components which acts as a catalyst. The disappearing rate of materials starts slowly due to the little amount of the catalyst produced while it maximizes as long as the amount of the catalyst is increased and then the rate drops again to a low value as the reactant is consumed. For each amount of the initial concentration of lead and the electric current supplied, the values of the rate of reaction and its constant were determined. The behavior of reaction along the duration of the experiment, as noted, was irregular belong to the values of initial lead concentration and current applied which may be explained by the uncontrolled processes of the formation and removing of the oxide layer above the cathode electrode, then the generation of catalyst as consequence. The present work studied an electrocoagulation reactor involved in a novel design of electrodes to explain the behavior of the autocatalytic reactions throughout the electrochemical reactor.

CC E

[1] AlJaberi, F., Y., Electrocoagulation using concentric tubes electrodes reactor for removal of lead from simulated wastewater, PhD Thesis in Chemical Engineering, University of Baghdad, 2018. [2] Carocci, A., Catalano, A., Lauria, G., Sinicropi, M. S., Genchi, G., Lead toxicity, antioxidant defense and environment, Reviews of environmental contamination and toxicology, Springer International Publishing, 238 (2016) 45-67.

A

[3] Efimova, N., Krasnopyorova, A. P., Yuhno, G. D., Scheglovskaya, A. A., Sorption of heavy metals by natural biopolymers, Adsorption Science & Technology , 35 (2017) 595-601. [4] Martin, S., Griswold, W., Human health effects of heavy metals, Center for Hazardous Substance Research, 15 (2009)1-6. [5] World health organization, Guidelines for drinking-Water quality, fourth ed., Geneva, 2011. [6] Barakat, M.A., New trends in removing heavy metals from industrial wastewater, Arabian Journal of Chemistry, 4 (2011) 361-377.

[7] Tripathi, A., Ranjan, M. R., heavy metal removal from wastewater using low cost adsorbents, Bioremediation and Biodegradation J., 6 (6) (2015) 1-5. [8] Coelho, L. M., Rezende, H. C., Coelho, L. M., Sousa, P. A.R., Melo, D. F.O., and Coelho, N. M. M., , Advances in bioremediation of wastewater and polluted soil bioremediation of polluted waters using microorganisms, First edition Naofumi Shiomi publication, (2015). [9] Wang, L. K., Hung, Y.T., Shammas, N. K., Handbook of environmental engineering: physicochemical treatment processes, First edition, The Humana Press Inc., Totowa, NJ, (2005).

IP T

[10] Yang, J., Membrane bioreactor for wastewater treatment , First edition ,bookboon Ltd., (2013). [11] Gunatilake, S.K., Methods of removing heavy metals from industrial wastewater, Journal of Multidisciplinary Engineering Science Studies, 1 (1) (2015) 12-18.

SC R

[12] Fu, F., Wang, Q., Removal of heavy metal ions from wastewaters: A review, Journal of Environmental Management, 92 (2011) 407-418.

U

[13] Kabdas, I., Arslan, T., Ölmez-Hanc T., Arslan-Alaton, I., Tünay, O., Complexing agent and heavy metal removals from metal plating effluent by electrocoagulation with stainless steel electrodes, Journal of Hazardous Materials, 165 (2009) 838-845.

N

[14] Joshi, N. C., Heavy metals, conventional methods for heavy metal removal, biosorption and the development of low cost adsorbent, European Journal of Pharmaceutical and Medical Research, 4 (2) (2017) 388-393.

M

A

[15] Tansel, B., New Technologies for water and wastewater treatment: A survey of secent patents, Recent Patents on Chemical Engineering, 1 (1) (2008) 17-26.

ED

[16] Moura, R. C. A., Bertuo, D. A., Ferreira, C. A., Amado, F. D. R., Study of chromium removal by the electrodialysis of tannery and metal-finishing effluents, International Journal of Chemical Engineering, ID 179312 (2012) 1-7.

PT

[17] Caprarescu, S., Corobea, M. C., Purcar, V., Spataru, C. I., Ianchis, R., Vasilievici, G., Vuluga, Z., San copolymer membranes with ion exchangers for Cu (II) removal from synthetic wastewater by electrodialysis, Journal of Environmental Sciences-China, 35 (2015) 27-37.

CC E

[18] Caprarescu S., Ianchis R., Radu A-L., Sarbu A., Somoghi R., Trica B., Alexandrescu E., Spataru C.-I., Fierascu R. C., Ion-Ebrasu D., Preda S., Atanase L.-I., Donescu D., Synthesis, characterization and efficiency of new organically modified montmorillonite polyethersulfone membranes for removal of zinc ions from wastewasters, Applied Clay Science, 137 (2017) 135142.

A

[19] Wan, D., Xiao, S., Cui, X., Zhang, Q., Song, Y, Removal of Cu 2+ from aqueous solution using proton exchange membrane by Donnan dialysis process, Environmental Earth Sciences, 73 (9) (2015) 4923-4929. [20] Olutoye, M. A., Alhamdu, J. A., Electrochemical separation of metal silver from industrial wastewater, Advances in Chemical Engineering and Science, 4 (2014) 396-400.

[21] Un, U. T., Ocal, S. E., Removal of heavy metals (Cd, Cu, Ni) by electrocoagulation, International Journal of Environmental Science and Development, 6 (6) (2015) 425-429.

[22] Walsh, F. C., Electrochemical technology for environmental treatment and clean energy conversion, Pure Appl. Chem., 73 (12) (2001) 1819-1837. [23] Cerqueria, A., Russo, C., Marques, R. C., Electroflocculation for Textile Wastewater Treatment, Brazilian Journal of Chemical Engineering, 26 (4) (2009) 659-668. [24] AlJaberi, F. Y., Mohammed, W. T., The most practical treatment methods for wastewaters: A systematic review, proceeding of 2ndInternational conference of science and Art University of Babylon and Liverpool John Moores University, UK, Mesopo. Environ. j., Special Issue E (2018) 1 -28.

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