Zinc Cementation of Heavy Metals from Electric Arc Furnace Dust Recycling Process Extracted by Hydrochloric Acid Solution
Zinc Cementation of Heavy Metals from Electric Arc Furnace Dust Recycling Process Extracted by Hydrochloric Acid Solution Chanwit Thititanagul1 , Porntip Lekpittaya2 and Sureerat Polsilapa3 Interdisciplinary Graduate Program in Advanced and Sustainable Environmental Engineering, Department of Chemical Engineering, Faculty of Engineering, Kasetsart University1 Department of Materials Engineering, Faculty of Engineering, Kasetsart University2,3 Email: [email protected], [email protected], [email protected]
Abstract The benefits of hydrochloric acid for selective leaching electric arc furnace (EAF) dust has been reported by many authors. Low concentration hydrochloric acid can extract zinc which presence as the majority element contained in the EAF dust while leaving the iron in the solid residue. After extraction, there are also hazardous elements that were leached into an aqueous solution such as lead and chromium. These two elements could affect the efficient currency in the electrolytic cell on the electrowinning process for zinc separation from the solution. Thus, in this study, the cementation process was investigated using zinc powder in order to cement the solute heavy metals in the zinc-rich solution prior to the further process. Then optimal conditions were found to be; Zn/Pb 3.0 molar ratio, the temperature at 60oC, and rotation speed at 500 rpm for 10 minutes. The final solution was very high purity (Pb and Cr concentration < 2 ppm) which was suitable for zinc deposition to produce metallic zinc.
Keywords: Zinc; Cementation; Electric Arc Furnace Dust; Hydrochloric Acid; Heavy Metals 24 วิศวกรรมสาร มก.
1. Introduction very stable structure of ZnFe2O4, and the emission of greenhouse gases are considered Steel has played an important role in as two main drawbacks of this method. world economics for ages. Many industrial sectors, Therefore, the combination of pyro-hydro- such as electronic devices, transportation, metallurgy was investigated [6,8,9]. A low mechanic, and construction, use steel as concentration of acid solution was reported a primary material. Most of the Thai steel to extract approximately 20 wt% of zinc from makers use a large amount of scrap material the EAF dust [5]. Other researchers have that is melted in an electric arc furnace at a o focused on ZnFe2O4 decomposition using very high temperature (>1,700 C) to produce reducing agents, such as carbon [6] and iron new steel alloys. The electric arc furnace [7], to lower the energy consumption in the (EAF) dust, a by-product is generated and process. It was reported that approximately typically collected by bag house filter and 70 wt% of zinc ferrite was transformed into accounts for approximately 1-2% of feedstock zinc oxide [6-9]. However, calcium oxide and [1]. It is reported that the main chemical eggshell, which was consists of calcium oxide composition of EAF dust consists of three as the main chemical composition, have been main compounds; zinc ferrite (ZnFe2O4), found to be an economical reducing agent zinc oxide (ZnO), and iron oxide (FexOy) [8,9]. Lime and eggshell were employed by [2]. X-ray fluorescence analysis reveals trace mixing with EAF dust in order to decrease elements, in the EAF dust, of lead (Pb), the temperature, in the pyrometallurgical chromium (Cr), cadmium (Cd), and process, for the decomposition of the very manganese (Mn) [3,4]. The zinc and other stable ZnFe2O4. The product of ZnFe2O4 hazardous elements in the EAF dust arise decomposition is ZnO, which is less stable from much of the scrap having been and is extractable by weak acidic solutions galvanized. Therefore, the EAF dust is [10,11]. Various acidic solutions have been classified as hazardous waste, and disposal studied, such as sulfuric acid (H2SO4), of which requires specific management. nitric acid (HNO3), and hydrochloric acid (HCl) However, the EAF dust has potential as a [5]. Low concentrations of HCl selectively secondary source of zinc and iron. Previous leaches zinc in solution leaving iron as solid research has reported on methods to extract residue [8]. Furthermore, using hydrochloric zinc from the EAF dust [4-9]. Pyrometallurgy acid as a leaching solution also gives a benefit has been widely studied to treat electric arc in further electrowinning processes. The furnace dust over the past years [3]. However, solution, after zinc extraction by HCl, high energy consumption a result of the contains ZnCl2, which could be used out- Zinc Cementation of Heavy Metals from Electric Arc Furnace Dust 25 Recycling Process Extracted by Hydrochloric Acid Solution right in zinc deposition for metallic zinc or zinc alloy production. After the extraction 2. Experimental process, it was reported that trace elements 2.1 Materials and Chemicals such as lead (Pb), copper (Cu), and cadmium Electric arc furnace dust, collected (Cd) are extracted into the solution as well by baghouse filter, was obtained from 13 [1,5]. These elements could reduce efficiency steel recycling factories in Thailand. Calcium in the electrowinning process in addition to oxide powder was obtained from DAEJUNG environmental issues. The cementation Ltd., South Korea, hydrochloric acid (37% process has been investigated for many w/v) from Merck KGaA Ltd., USA and applications, mainly for the removal of heavy zinc powder with a purity of 99.9% and metals from solution. A well-known cementa- an average size of approximately 1.27 μm tion process is the Merrill-Crowe process for from AJAX Finechem Ltd., Australia. HCl, removal of gold from the solution [11]. The zinc powder, and CaO were of analytical advantage of zinc cementation not only for grade (AR) and laboratory-grade (LR). removing heavy metals in the solution but 2.2 Analytical instruments recovery these valuable metals back in solid- The phases of the solid samples were state. Zinc was found to be a potential mate- analyzed by X-ray diffraction (XRD) (Philip rial for cementation due to its high galvanic series X’pert). The conditions for analysis θ o o series. It is good at reducing electrons from were 2 , 20 to 70 , the step size was 0.02, the present time 1 second, CuKα radiation other metals [10,11]. The investigation of fac- was used. Chemical composition of the EAF tors affecting zinc cementation of lead and dust, calcium oxide, and zinc powder was chromium in low concentration hydrochloride analyzed by X-ray fluorescence (XRF) (Horiba acid solution prior to the electrowinning pro- XGT-5200). Each sample was measured at 3 cess and the kinetics involved are the main points and the average value of wt% by ele- objectives of this research. Operating vari- ments was calculated. The conditions were; ables of the Zn/Pb stoichiometric ratio, tem- live time: 100 second, processing time: P2, perature, stirring speed and cementation time XGT Dia: 1.2 mm, X-ray tube vol: 50 kV, were investigated in order to maximize the X-ray filter: 5 Element, Cell: Nonexistence. Atomic absorption spectrophotometer (AAS) removal of heavy metals from the aqueous (Perkin Elmer with GBC Avanta Ver 2.01) solution. Further removal after cementation was used to analyze the chemical concentra- could be provided by an electrowinning pro- tion of the aqueous solution. Each sample cess to produce metallic zinc or zinc alloy for was measured three times and reported by use as a primary material for many industries. the average value with part per million (ppm). 26 วิศวกรรมสาร มก.
2.3 Methods stirrer with temperature monitored by ther- Three steps were used to extract zinc mometer. The optimum conditions for zinc in this study. The EAF dust was firstly extraction have been found to be 0.5M, HCl, calcined using CaO as a reducing agent, a solid/liquid ratio of 1:10, a solution temper- o in order to transform the ZnFe2O4 to ZnO. ature of 60 C, stirring speed of 900 rpm, and The resultant EAF dust was then leached extraction time of 20 minutes [5][8]. Atom- by a low concentration HCl solution. ic absorption spectrophotometer (AAS) was The heavy metals now leached out used to determine the concentration of lead underwent was cementation by zinc powder. and chromium leached into the aqueous so- 2.3.1 Calcining lution prior to the cementation process. After The phases present in the EAF leaching, solid residue was dried and dust samples determined by XRD. They characterized by XRD to confirm ZnO were then mixed with CaO: ZnFe2O4 molar extraction. ratio of 1:2 and hand pressed into a disk of 2.3.3 Cementation approximately 1 cm radius and 0.5 cm thick. Two liters of the leachant was The EAF dust mixed with CaO was calcined separated into 100 ml. aliquots for each at 800oC for 2 hours in Modultemp furnace experiment. After analysis of the leachant to at a 10oC/min heating rate. The resultant determine the concentration of the lead, material was analysed by XRD to confirm zinc powder was added in the molar ratios phase transformation and comparative (Zn/Pb) of 1.5, 3.0, and 4.5. The solution o intensities of ZnFe2O4 to ZnO peaks. temperatures were varied between 40 C, 2.3.2 Leaching 50oC, and 60oC. The effect of stirring The calcined EAF dust was leached speed was investigated at 100, 500, and by HCl solution. The leaching was carried out 900 rpm. The measurement of Pb and Cr based on the work of previous researchers. concentrations were taken initially, then after The solution was heated on hot plate- magnetic 10 minutes and 30 minutes cementation time. 700 absorption spectrophotometer (AAS) was used 1 – ZnFe2O4 , 2 – ZnO, 3 – Ca2Fe2O5 Zinc Cementation of Heavy Metals from Electric1 Arc Furnace Dust to determine the concentration of lead and 600 4 – CaO , 5 – Fe3O427 absorptionchromium spectrophotometerleached into the aqueous (AAS) wassolution used 700 Recycling Process Extracted500 by Hydrochloric Acid1 – ZnFe Solution2O4 , 2 – ZnO, 3 – Ca2Fe2O5 prior to the cementation process. After leaching, 1 to determine the concentration of lead and 600 4 – CaO , 5 – Fe3O4 solid residue was dried and characterized by 400 chromium leached into the aqueous solution 700 absorption spectrophotometer (AAS) was used 500 XRD to confirm3. Results ZnO and extraction. discussion 1 – ZnFe2O4 , 2 – ZnO, 3 – Ca2Fe2O5 prior to the cementation process. After leaching, 300 1 to determine the concentration of lead and 600Intensity 4 – CaO , 5 – Fe3O4 400 1 solid residue was dried and characterized by 2 chromium2.3.3 leached Cementation3.1 into Chemical the aqueous composition solution and 200 1 1 XRD to confirm ZnO extraction. 500 2 Two liters of the leachant was separated 300 1 prior to the cementation process. After leaching, Intensity 2 phase analysis 100 1 1 into 100 ml. aliquots for each experiment. 400 2 1 2 solid residue2.3.3 Cementation was dried and characterized by 200 1 1 2 2 X-ray fluorescence was used to 2 2 XRDAfter to Twoanalysis confirm liters of ZnO ofthe the leachantextraction. leachant to wasdetermine separated the 0 1 300 20 30 2 40 50 60 70 Intensity 100 1 concentrationinto 100analyze ml. ofaliquots thethe chemicallead, for zinceach composition powderexperiment. was of the 1 2θ 1 2 2 2 2 2.3.3 Cementation 200 2 1 1 addedAfter analysisin EAFthe molar dust,of the EAFratios leachant dust (Zn/Pb) tomixed determine of with 1.5, CaO, 3.0,the zinc 0 2 20 30 40 1 50 60 70 Two liters of the leachant was separated Figure 1 XRD2 pattern of EAF dust sample concentrationand 4.5. The solution of the temperatureslead, zinc powder were varied was 100 1 into 100 particle,ml.o aliquots ando CaO for powder.eacho experiment. Table 1 shows a from factories2θ 1 2 2 2 addedbetween in 40theC, molar 50 C, ratios and (Zn/Pb)60 C. The of effect1.5, 3.0, of 2 After analysishigh ofconcentration the leachant of to zinc determine in the thEAFe dust 0 andstirring 4.5. speed The solution was investigated temperatures at 100, were 500, varied and 20Figure 130XRD pattern40 of EAF50 dust sample60 70 concentration of the lead, zinc powder was between900 rpm. at40 Theo32.163C, 50measuremento C,wt%. and As 60 oto C.of beThe Pb expected, effectand Crof there from factories2θ added in the molar ratios (Zn/Pb) of 1.5, 3.0, stirringconcentrations speedwas awas werehigh investigated leveltaken of initially, iron at 100,available then 500, after andat 31.681 and 4.5. The solution temperatures were varied 700FigureFigure 1 XRD1 XRD pattern pattern of EAF of EAFdust sampledust 10 minutes and 30 minutes cementation time. 1 – ZnFe2O4 , 2 – ZnO, 3 – Ca2Fe2O5 900 rpm.wt%. oThe The measuremento concentrationo of ofPb theand hazardous Cr from factories between 40 C, 50 C, and 60 C. The effect of 4 – CaO , 5 – Fe O concentrations were taken initially, then after 600 sample from factories 3 4 stirring speedelements, was investigated lead and chromium, at 100, 500, were and found to 700 103. Resultsminutes and and discussion30 minutes cementation time. 500 1 – ZnFe2O4 , 2 – ZnO, 3 – Ca2Fe2O5 900 rpm. The measurement of Pb and Cr be 2.602 wt% and 0.200 wt% respectively. 600 4 – CaO , 5 – Fe3O4 concentrations3.1 Chemical were takencomposition initially, andthen phaafterse 400 700 3. Results and discussion The phases present in the EAF dust 500 10analysis minutes and 30 minutes cementation time. 1 – ZnFe2O4 , 2 – ZnO, 3 – Ca2Fe2O5 300
Intensity 2 before and after calcining were determined 600 4 – CaO , 5 – Fe3O4 X3.1-ray Chemical fluorescence composition was used andto analyze phase 400 2 200 3.analysisResultsby and XRD discussion and the resultant diffractographs are 500 the chemical composition of the EAF dust, 300 4 2 Intensity 12 EAF dust mixed with CaO, zinc particle, and 100 2 32 4 2 3.1X- rayshownChemical fluorescence in Figurecomposition was1 and used Figureand to analyzepha 2. sePrior to 400 1 1 1 2 CaO powder. Table 1 shows a high concentration 200 3 3 4 2 analysisthe chemicalcalcination composition the major ofphase the present EAF isdust, ZnFe 2O4, 0 4 2 300 20 30 1 40 50 60 70 EAFof zinc dust in themixed EAF with dust CaO, at 32.163 zinc particle, wt%. As and to Intensity 100 2 32 1 4 12 2 X-raythe fluorescence only other phase was present used to being analyze ZnO. After 3 2 1 2θ 3 4 2 CaObe expected, powder. Tablethere 1 wasshows a ah ighhigh levelconcentration of iron 200 the chemical composition of the EAF dust, 0 20 Figure30 2 XRD4 40pattern of50 EAF2 dust60 70 ofavailable zinc incalcination, at the 31.681 EAF wt%.dustthe majorat The 32.163 concentrationphase wt%. present As oftois now 1 EAF dust mixed with CaO, zinc particle, and 100 after treatment2θ3 by2 CaO4 2 bethe expected,hazardous there elements, was alead high and level chromium, of iron 3 1 1 3 1 22 CaO powder.ZnO. Table The 1ZnFe shows2O4 a phasehigh concentration is still present but 4 availablewere found at 31.681to be 2.602 wt%. wt%The concentrationand 0.200 wt% of 0 Figure 2 XRD pattern of EAF dust of zinc in atthe a EAFmuch dust reduced at 32.163 level. wt%.Indicating As to decom 20Figure 302 XRD pattern40 of50 EAF dust60 70 therespectively. hazardous elements, lead and chromium, after treatment by CaO be expected, there was a high level of iron 2θ were foundTheposition phases to be ofpresent 2.602 ZnFe 2inOwt% 4the to EAFandZnO 0.200dusthas takenbefore wt% place. after treatment by CaO available at 31.681 wt%. The concentration of 700 Figure 2 XRD pattern of EAF dust respectively.and after calcining were determined by XRD 1 – ZnFe2O4 , 2 – ZnO, 3 – Ca2Fe2O5 the hazardous elements, After HCl lead leaching and chromium, to extract the after treatment by CaO and theThe resultant phases presentdiffractographs in the EAF are dust shown before in 600 4 – CaO , 5 – Fe3O4 were foundzinc, to thebe 2.602solid residue wt% andwas 0.200analysed wt% by XRD. andFigure after 1 andcalcining Figure were 2. Prior determined to calcination by XRD the 700 respectively. 500 1 – ZnFe2O4 , 2 – ZnO, 3 – Ca2Fe2O5 major phaseComparison present isof ZnFeFigure2O 34 , withthe onlyFigure other 2 shows and the resultant diffractographs are shown in 600 4 – CaO , 5 – Fe3O4 The phases present in the EAF dust before phase present being ZnO. After calcination, the 400 Figure 1 theand intensityFigure 2. of Prior the toZnO calcination peaks decreasing the 700 and after calcining were determined by XRD 500 major phase present is now ZnO. The ZnFe2O4 1 – ZnFe2O4 , 2 – ZnO, 3 – Ca2Fe2O5 major phase present is ZnFe2O4, the only other 300
significantly, suggesting the leaching process Intensity and the resultant diffractographs are shown in 600 4 – CaO , 5 – Fe3O4 phase presentis still beingpresent ZnO. but After at a calcination,much reduced the 400 Figure 1 andis successful.Figure 2. PriorFigure to calcination3 shows thethe major 200 level.major Indicatingphase present decomposition is now ZnO. of The ZnFe ZnFe2O24O to4 500 300 3 2 major phase present is ZnFe2O4, the only other Intensity 2 phaseZnO has is peaktakenstill presentto place. be that but belonging at a much to Fereduced3O4. Atomic 100 2 phase present being ZnO. After calcination, the 400 3 2 2 2 level. AfterIndicating HCl decompositionleaching to extract of ZnFe the2 Ozinc,4 to 200 major phaseabsorption present spectrophotometryis now ZnO. The ZnFegives2 Othe4 initial 0 3 2 the solid residue was analysed by XRD. 300 20 30 2 40 50 60 70 ZnO has taken place. Intensity 100 2 phaseComparison is stillconcentrations ofpresent Figure but 3of withatPb aand Figuremuch Cr inreduced2 theshows aqueous 2θ3 2 2 2 After HCl leaching to extract the zinc, 200 level. Indicating decomposition of ZnFe2O4 to 0 the intensitysolidsolution residue of as the 40.48 was ZnO ppm analysed peaks and 0.12 decreasing ppmby XRD.respectively. Figure20 330 XRD3 2 pattern40 of50 EAF dust60 70 ZnO has taken place. Figure2 3 XRD pattern of EAF dust Comparisonsignificantly, ofsuggesting Figure 3 withthe leaching Figure 2process shows 100 after2 leaching2θ by HCl After HCl leaching to extract the zinc, after leaching by3 2 HCl 2 2 theis successful. intensity Figureof the 3 ZnOshows peaks the major decreasing peak to 0 the solid residue was analysed by XRD. 20 Figure30 3 XRD40 pattern of50 EAF dust60 70 significantly,be that belonging suggesting to Fe3O the4. Atomic leaching absorption process Comparison of Figure 3 with Figure 2 shows after leaching2θ by HCl spectrophotometryis successful. Figure gives 3 shows the initial the majorconcentrations peak to the intensity of the ZnO peaks decreasing ofbe Pbthat and belonging Cr in the to aqueousFe3O4. Atomic solution absorption as 40.48 Figure 3 XRD pattern of EAF dust significantly, suggesting the leaching process spectrophotometryppm and 0.12 ppm gives respectively. the initial concentrations after leaching by HCl is successful. Figure 3 shows the major peak to of Pb and Cr in the aqueous solution as 40.48 be that belonging to Fe3O4. Atomic absorption ppm and 0.12 ppm respectively. spectrophotometry gives the initial concentrations of Pb and Cr in the aqueous solution as 40.48 ppm and 0.12 ppm respectively. Table 1 Chemical composition of EAF dust, Zinc powder, CaO by X-ray fluorescence
Elements K Ca Cr Mn Fe Cu Zn Pb O wt.% EAF dust 1.540 4.991 0.200 1.570 31.681 0.202 32.163 2.602 25.052 Zinc 0 0 0 0 0.030 0 99.970 0 0 powder CaO 0 71.469 0 0 0 0 0 0 28.581 powder
3.2 Effects of operating factors to 45 cementation rate 40 1.5 3.0 35 4.5 3.2.1 Zn/Pb mole ratio 30 To investigate the effect of the Zn/Pb 25 ratio, temperature and stirring speed were 20 o maintained at 60 C and 900 rpm. Figure 4 and 15 10
Figure 5 show the effect of molar ratio as Pb concentration (ppm) a function of time. Increasing the Zn/Pb introduces 5 more zinc ions into solution could increase the 0 0 10 20 30 40 cementation rate. High zinc particle in the Time (minutes) solution meaning that increasing the chemical surface area of reaction between zinc and Figure 4 Residual Pb concentration as a function of heavy metals. time for various Zn/Pb ratios Increasing the Zn/Pb ratio, a high 28 วิศวกรรมสาร มก. amount of zinc powder added into solution also 0.14 increases the chance of molecules collision 0.12 1.5 together affecting the chemical reaction 3.0 0.1 4.5 between Zn0 in the solution and heavy metals. Table 1 Chemical composition of EAF dust, Zinc powder, CaO by X-ray fluorescence 0.08 Table 1 Chemical composition of EAF dust, ZincThe powder, cementation CaO reactionby X-ray proceeds fluorescence rapidly up to 10 minutes. The concentration of heavy metals, 0.06 Elements detected by atomic absorption spectrophotometry K Ca Cr Mn Fe Cu Zn Pb O 0.04
wt.% are shown in Table 2. The cementation rate Cr concentration (ppm) 0.02 EAF dust 1.540 4.991 0.200 1.570 consistently31.681 proceeds0.202 after32.163 10 minutes2.602until the25.052 concentration of lead and chromium 1.54 ppm 0 Zinc 0 5 10 15 20 25 30 35 0 0 0 0 and0.030 0.007 ppm respectively.0 99.970 Therefore,0 Zn/Pb 0 Time (minutes) powder molar ratio 3.0 resulted in the optimal CaO 0 71.469 0 0 condition0 for zinc0 cementation.0 0 28.581 Figure 5 Residual Cr concentration as a function of powder time for various Zn/Pb ratios
Table 1 Chemical3.2 Effectscomposition of operating of EAF dust,factors Zinc to powder,TableTable CaO 2 The45 by concentrationX-ray fluorescence of Pb andand Cr inin thethe Table 3.21 Chemical Effectscomposition of operating of EAF factors dust, Zinc to powder, CaO by X-ray fluorescence 3.2.2 Temperature leachant before and after cementation which cementationcementation rate rate leachant 40before and after cementation which 1.5 Elements was performed under the optimal condition 3.0 The experiment was performed at a Zn/Pb Elements 3.2.1K Zn/PbCa mole ratioCr Mn Fewas performed35Cu underZn the optimalPb conditionO wt.% K Ca Cr Mn Fe Cu Zn Pb O 4.5 ratio 3.0 and stirring speed 900 rpm. The wt.%3.2.1 Zn/Pb mole ratio 30 EAF dust 1.540To investigate4.991 the 0.200effect of 1.570the Zn/ 31.681 0.202 Concentration32.163 2.602 (ppm)25.052 concentration of the heavy metals, Pb and Cr, EAF dust 1.540 4.991 0.200 1.570 31.681 250.202 32.163 2.602 25.052 ZincTo investigate the effect of the Zn/Pb After in the solution decreased below 2 ppm as seen ZincPb ratio, 0 temperature0 and 0 stirring 0speed 0.030Elements0 Before99.970 0 0 ratio,powder temperature0 and0 stirringo 0 speed 0were 0.030 20 0 99.970 0 0 by Figure 6 and Figure 7 in the first 10 minutes powder cementation for CaOwere maintainedo at 60 C and 900 rpm. 15 cementation of zinc cementation. The higher temperatures maintainedCaO at0 60 C and71.469 900 rpm.0 Figure 40 and 0 0 0 0 10 minutes28.581 powderFigure 4 0and Figure71.469 5 show0 the effect0 of 0 Pb 10 0 40.480 0 1.5428.581 show a faster cementation for both of Pb and Figure 5 show the effect of molar ratio as Pb concentration (ppm) powder Cr. The results show that 60oC for Pb and Cr a functionmolar ofratio time. as Increasing a function the of Zn/Pb time. introducesIncreasing Cr 5 0.12 0.007 45 cementation are the optimal temperatures for morethe3.2 zinc Zn/PbEffects ions intointroduces of solution operating more could factorszinc increase ions to theinto 45 0 3.2 Effects of operating factors to 40 0 10 20 1.530 40 their cementation. The increase in temperature cementation rate 40 1.5 cementationcementation raterate. High zinc particle in the Time (minutes) 3.0 providing an increase in cementation rate can solution could increase the cementation rate. 35 3.0 solution3.2.1 meaning Zn/Pb mole that ratioincreasing the chemical 35 4.5 High3.2.1 zincZn/Pb particle mole ratioin the solution meaning 30 4.5 surface area of reaction between zinc and 30 Figure 4 Residual Pb concentration as a function of To investigate the effect of the Zn/Pb 25 thatTo investigateincreasing thethe effectchemical of the surface Zn/Pb area 25 heavy metals. 20 time for various Zn/Pb ratios ratio, temperature and stirring speed were 20 ratio,of temperatureIncreasing reaction obetween andthe stirring Zn/Pbzinc and speedratio, heavy werea metals.high maintained at 60oC and 900 rpm. Figure 4 and 15 maintained at 60 C and 900 rpm. Figure 4 and 15 0.14 amount of zinc powder added into solution also 10 Figure 5 showIncreasing the effect the of Zn/Pb molar ratio, ratio aas high Pb concentration (ppm) 10
Figure 5 show the effect of molar ratio as Pb concentration (ppm) 1.5 aincreases function of thetime. chance Increasing of themolecules Zn/Pb introduces collision 5 0.12 a functionamount of time. of zincIncreasing powder the Zn/Pbadded introducesinto solution 5 3.0 moretogether zinc ionsaffecting into solution the couldchemical increase reaction the 0 more zinc ions into solution could increase the 0 0 0.1 10 20 30 40 4.5 cementation 0rate. High zinc particle in the 0 10 20 30 40 cementationbetweenalso increasesZn rate.in the Highthe solution chancezinc andparticle of heavymolecules in metals.the col- Time (minutes) solution meaning that increasing the chemical 0.08 Time (minutes) solutionThe lisioncementation meaning together that reaction affecting increasing proceeds the the chemical chemical rapidly reac up- surface area of reaction between zinc and FigureFigure 4 Residual4 Residual Pb concentration Pb concentration as a function as ofa surfaceto 10 minutes. area of The reaction concentration between of heavyzinc andmetals, Figure 40.06 Residual Pb concentration as a function of heavytion metals. between Zn0 in the solution and heavy time for various Zn/Pb ratios heavydetected metals. by atomic absorption spectrophotometry function timeof time for various for various Zn/Pb ratios Zn/Pb ratios Increasing the Zn/Pb ratio, a high 0.04 metals.Increasing The thecementation Zn/Pb ratio,reaction a highproceeds 0.14 amountare shown of zinc in powder Table added2. The into cementation solution also rate 0.14 Cr concentration (ppm) amount of zinc powder added into solution also 0.02 0.12 1.5 increasesconsistentlyrapidly the up proceedschance to 10 of afterminutes. molecules 10 minutes The collision concentrauntil the- 1.5 increases the chance of molecules collision 0.12 3.0 togetherconcentrationaffecting of lead the and chemical chromium reaction 1.54 ppm 0 3.0 0.1 4.5 togethertion affectingof0 heavy metals,the chemical detected reaction by atomic 0.1 0 5 10 15 20 25 30 35 betweenand 0.007 Zn 0ppmin the respectively. solution and Therefore, heavy metals. Zn/Pb 4.5 between Zn in the solution and heavy metals. 0.08 Time (minutes) The cementationabsorption reactionspectrophotometry proceeds rapidly are upshown 0.08 Themolar cementation ratio 3.0 reaction resulted proceeds in rapidlythe optimal up to 10 minutes. The concentration of heavy metals, 0.06 tocondition 10 inminutes. Table for The zinc2. concentrationThe cementation. cementation of heavy rate metals, consist- 0.06 detected by atomic absorption spectrophotometry Figure 5 Residual Cr concentration as a function of detected by atomic absorption spectrophotometry 0.04 time for various Zn/Pb ratios ently proceeds after 10 minutes until the 0.04 are shown in Table 2. The cementation rate Cr concentration (ppm)
are shown in Table 2. The cementation rate Cr concentration (ppm) consistently proceeds after 10 minutes until the 0.02 consistentlyTableconcentration 2 The proceeds concentration of after lead 10 andminutesof Pb chromium anduntil Cr the in 1.54the 0.02 concentration of lead and chromium 1.54 ppm 0 concentration of lead and chromium 1.54 ppm 0 0 3.2.25 10Temperature15 20 25 30 35 andleachant 0.007ppm beforeppmand respectively.0.007 and afterppm Therefore,cementationrespectively. Zn/Pb whichThere - 0 5 10 15 20 25 30 35 and 0.007 ppm respectively. Therefore, Zn/Pb Time (minutes) molarwas performed ratio 3.0 under resulted the optimal in the conditionoptimal Time (minutes) molarfore, ratio Zn/Pb 3.0 molarresulted ratio in3.0 the resulted optimal in the Figure 5The Residual experiment Cr concentration was performed as aat a Zn/Pb condition for zinc cementation. Figureratio 5 Residual 3.0 and Cr concentrationstirring speed as a function 900 ofrpm. The conditionoptimal for zinccondition cementation. for zinc cementation. Figure 5 Residual Cr concentration as a function of functionconcentration timeof time for various offor thevarious Zn/Pb heavy ratios Zn/Pb metals, ratios Pb and Cr, Concentration (ppm) time for various Zn/Pb ratios in the solution decreased below 2 ppm as seen Table 2 The concentration of Pb and CrAfter in the TableElements 2 The concentrationBefore of Pb and Cr in the 3.2.2 Temperature leachant before and after cementationcementation which for by3.2.2 Figure Temperature 6 and Figure 7 in the first 10 minutes leachant beforecementation and after cementation which was performed under the optimal condition10 minutes ofThe zinc experiment cementation. was performed The higher at a temperaturesZn/Pb was performed under the optimal condition The experiment was performed at a Zn/Pb Pb 40.48 1.54 ratioshow 3.0 anda faster stirring cementation speed 900 for rpm. both The of Pb and ratio 3.0 and stirring speed 900 orpm. The concentrationCr. The resultsof the heavyshow metals,that 60 PbC andfor PbCr, and Cr Cr Concentration0.12 (ppm)0.007 concentration of the heavy metals, Pb and Cr, Concentration (ppm) in thecementation solution decreased are the below optimal 2 ppm temperatures as seen for After in the solution decreased below 2 ppm as seen Elements Before After by Figure 6 and Figure 7 in the first 10 minutes Elements Before cementation for by Figuretheir cementation.6 and Figure 7 Thein the increase first 10 minutesin temperature cementation cementation for of zinc cementation. The higher temperatures cementation 10 minutes of zincproviding cementation. an increase The higher in cementation temperatures rate can 10 minutes show a faster cementation for both of Pb and Pb 40.48 1.54 show a faster cementation for both of Pb and Pb 40.48 1.54 Cr. The results show that 60oC for Pb and Cr Cr 0.12 0.007 Cr. The results show that 60oC for Pb and Cr Cr 0.12 0.007 cementation are the optimal temperatures for cementation are the optimal temperatures for their cementation. The increase in temperature their cementation. The increase in temperature providing an increase in cementation rate can providing an increase in cementation rate can Zinc Cementation of Heavy Metals from Electric Arc Furnace Dust 29 Recycling Process Extracted by Hydrochloric Acid Solution
3.2.2 Temperature 3.2.3 Stirring Speed The experiment was performed at a To investigate the effect of stirring Zn/Pb ratio 3.0 and stirring speed 900 rpm. speed, a Zn/Pb ratio of 3.0 was employed The concentration of the heavy metals, Pb and and a temperature at 60oC. The stirring Cr, in the solution decreased below 2 ppm speed has little effect on the cementation as seen by Figure 6 and Figure 7 in the first kinetics for the Pb, but an increasing 10 minutes of zinc cementation. The higher in speed increases the rate of removal of temperatures show a faster cementation the Cr. Theoretically, increasing stirring for both of Pb and Cr. The results show speed from 100 rpm to 900 rpm should that 60oC for Pb and Cr cementation are the increase the cementation rate because of at optimal temperatures for their cementation. higher speed there would be an increase in The increase in temperature providing an molecule collisions. As seen in Figure 8 increase in cementation rate can simply be and Figure 9, the concentration of Pb and simplysimply be be explained explained byby thethe increaseincrease in kinetics formingforming metalmetal oxideoxide especiallyespecially leadlead oxideoxide explaineddue to the moleculesby the increase moving faster,in kinetics increasing due Cr couldcould impedebe closely the chemical reduced reactio belown with2 ppm. zinc todue the to themolecules molecules moving moving faster,faster, increasingincreasing Figurecould 8 andimpede Figure the chemical9 show at reactio 500 rpmn with give zinc collisioncollision frequency frequency andand collisioncollision moremore energy. particles whichwhich isis occurredoccurred herehere as as well. well. The The collision frequency and collision more energy. thecementation best result efficiencyof Pb and at veryCr cementation. high rotation 45 cementation efficiency at very high rotation 45 speed could be lower than low rotation speed. 40 Thespeed results could were be lowercompared than lowto rotationother inves speed.- 40 40oC 40oC 35 50oC tigations45 [12,13]. Theory states that when 35 o 50oC 45 30 60 C o 40 30 60 C 100 rpm stirrer was40 rotated at very high speed100 rpm it 25 35 500 rpm 25 35 500 rpm 20 could increase the dissolution of the 900oxygenrpm 30 900 rpm 20 30 15 gas into25 the solution. The side reaction 15 25 10
Pb concentration (ppm) 20 10 between metals and oxygen forming metal Pb concentration (ppm) 20 5 15 simply be explained5 by the increase in kinetics forming metal15 oxide especially lead oxide 0 oxide especially10 lead oxide could impede the
0 5 10 15 20 25 30 35 40 Pb concentration (ppm) due to the molecules0 moving faster, increasing could impede10 the chemical reaction with zinc 0 5 10 15Time (minutes)20 25 30 35 40 chemicalPb concentration (ppm) 5 reaction with zinc particles which Time (minutes) 5 collision frequency and collision more energy. particles which0 is occurred here as well. The is occurred0 here5 10as 15well.20 The25 cementation30 35 40 Figure 6 Residual Pb concentration as a function of cementation0 efficiency at very high rotation Figure 6 Residual Pb concentration as a function of 0 5 10 Time15 (minutes)20 25 30 35 40 45 Figure 6 timeResidual for various Pb temperatureconcentration as a efficiency at very high rotation speed time for various temperature speed could be lower thanTime low(minutes) rotation speed. 40 function of time for various temperatur40oC couldFigure be lower 8 Residual than Pb lowconcentration rotation as speed.a function of 35 0.14 50oC 45Figure 8 Residualtime for variousPb concentration stirring speed as a function of 0.14 o 30 60 C 0.12 40 time for various stirring speed100 rpm 40oC 25 0.12 500 rpm 4050oC 35 0.1 0.14 o 900 rpm 20 5060oC 30 0.1 0.14 o 0.08 60 C 0.12 100 rpm 15 25 0.08 0.12 500100 rpmrpm 10 0.06 0.1
Pb concentration (ppm) 20 900500 rpm rpm 5 0.06 0.1 0.04 15 0.08 900 rpm 0 0.04 Cr concentration (ppm) 10 0.08 0 0.025 10 15 20 25 30 35 40 Pb concentration (ppm) 0.06
Cr Cr concentration (ppm) Time (minutes) 5 0.02 0.06 0 0.04 0 5 10 15 20 25 30 35 0 0 0 Cr concentration (ppm) 0.04 5 10 15 20 25 30 35 40 Figure 6 Residual Pb concentrationTime (minutes) as a function of 0.02 0 5 10 15 20 25 30 35 time for various temperature Cr concentration (ppm) Time (minutes) Time (minutes) 0.02 0 FigureFigure 7 7Residual Residual Cr concentration Cr concentration as a function as ofa Figure 80 Residual5 10 Pb 15concentration20 25 30 as a35 Figure 7 Residualtime for Cr various concentration temperature as a function of Figure 8 Residual0 Pb concentrationTime (minutes) as a function of 0.14 function of time for various temperature function timeof0 timefor5 various for10 various stirring15 20speedstirring25 speed30 35 time for various temperature Time (minutes) 0.12 3.2.3 Stirring Speed 40oC Figure 9 Residual Cr concentration as a function of 50oC Figure 9 Residualtime for variousCr concentration stirring speed as a function of 0.1 3.2.3 Stirring Speed 0.14 To investigate the effect of stirring60oC speed, time for various stirring speed
0.08 a Zn/PbTo investigateratio of the3.0 effect was employedof stirring speed, and 0.12 3.3 Cementation kinetics 100 rpm o aa Zn/Pb temperatureratio ofat 3.0 60 wasC. The employed stirring speed and 500 rpm 0.06 0.1 3.3 Cementation kinetics ahas temperature little effect onat the 60 cementationoC. The stirring kinetics speed for The rate of reaction between heavy900 rpm metals 0.04hasthe little Pb, buteffect an onincreasing the cementation in speed kinetics increases for and0.08 moreThe noble rate of metals reaction has between been investigated heavy metals in Cr Cr concentration (ppm) 0.02thethe Pb,rate but of anremoval increasing of the in Cr. speed Theoretically, increases variousand0.06 more studies noble [12 metals-14]. has been investigated in increasing stirring speed from 100 rpm to 900 variousHowever, studies [12side- 14].reaction with the presence the0 rate of removal of the Cr. Theoretically, 0.04 rpm0 should5 10increase15 the20 cementation25 30 rate35 because of oxygen in the solution was not considered increasing stirring speed from 100 rpm to 900 Cr concentration (ppm) However, side reaction with the presence rpmof at should higher increase speedTime there(minutes) the cementation would be an rate increase because in forof0.02 oxygenthis study. in Thus,the solution in this work,was not the consideredfollowing molecule collisions. As seen in Figure 8 and heterogeneous first-order rate equation was Figureof 7at Residual higher Crspeed concentration there would as a befunction an increase of in for0 this study. Thus, in this work, the following Figure 9, the concentration of Pb and Cr could applied0 to5 calculate10 15 the rate20 constant.25 30 35 moleculetime forcollisions. various temperatureAs seen in Figure 8 and heterogeneous firstTime-(minutes)order rate equation was be closely reduced below 2 ppm. Figure 9, the concentration of Pb and Cr could applied to lncalculate [A] – ln the [A 0rate] = -constant.kt (1) be closelyFigure reduced 8 and below Figure 2 9ppm. show at 500 rpm FigureWhere 9 Residual A is Cr the concentration concentration as a offunction lead and of 3.2.3 Stirring Speed ln [A] – ln [A0] = -kt (1) give Figurethe best 8 result and Figureof Pb and9 show Cr cementation. at 500 rpm time forchromium various stirring at time speed t. ToThe investigate results were the compared effect of to stirring other investigations speed, Where A is the concentration of lead and give the best result of Pb and Cr cementation. chromium at time t. a Zn/PbThe[12,13 resultsratio]. Theory wereof 3.0 compared states was employedthat to other when investigations stirrer and was 3.3 CementationThe rate constant kinetics (k) of the reaction was rotated at very higho speed it could increase the determined by the slope of the graph between a temperature[12,13]. Theoryat 60 statesC. The that stirring when stirrerspeed was The rate constant (k) of the reaction was dissolution of the oxygen gas into the solution. the relationship of ln[concentration] and time. has littlerotated effect at onvery the high cementation speed it could kinetics increase for the determinedThe rate of by reaction the slope between of the heavy graph metals between The side reaction between metals and oxygen From the Figure 10 and Figure 11, the results the Pb,dissolution but an increasing of the oxygen in speed gas into increases the solution. and morethe relationship noble metals of hasln[concentration] been investigated and time.in the rateThe of side removal reaction of betweenthe Cr. Theoretically,metals and oxygen variousFrom studies the Figure [12-14]. 10 and Figure 11, the results increasing stirring speed from 100 rpm to 900 However, side reaction with the presence rpm should increase the cementation rate because of oxygen in the solution was not considered of at higher speed there would be an increase in for this study. Thus, in this work, the following molecule collisions. As seen in Figure 8 and heterogeneous first-order rate equation was Figure 9, the concentration of Pb and Cr could applied to calculate the rate constant. be closely reduced below 2 ppm. ln [A] – ln [A0] = -kt (1) Figure 8 and Figure 9 show at 500 rpm Where A is the concentration of lead and give the best result of Pb and Cr cementation. chromium at time t. The results were compared to other investigations [12,13]. Theory states that when stirrer was The rate constant (k) of the reaction was rotated at very high speed it could increase the determined by the slope of the graph between dissolution of the oxygen gas into the solution. the relationship of ln[concentration] and time. The side reaction between metals and oxygen From the Figure 10 and Figure 11, the results simply be explained by the increase in kinetics forming metal oxide especially lead oxide due to the molecules moving faster, increasing could impede the chemical reaction with zinc collision frequency and collision more energy. particles which is occurred here as well. The cementation efficiency at very high rotation 45 speed could be lower than low rotation speed. 40 40oC 35 50oC 45 o 30 60 C 40 100 rpm 25 35 500 rpm 900 rpm 20 30
15 25
10
Pb concentration (ppm) 20
5 15
0 10
0 5 10 15 20 25 30 35 40 Pb concentration (ppm) Time (minutes) 5
0 Figure 6 Residual Pb concentration as a function of 0 5 10 15 20 25 30 35 40 time for various temperature Time (minutes)
Figure30 8 วิศวกรรมสารResidual Pb concentration มก. as a function of 0.14 time for various stirring speed show the cementation rate constant (k) of Pb 4. Conclusion 0.12 o 40oC andshow Cr. the At cementation t1, temperature rate constant 40 C (313.15K), (k) of Pb 4. ConclusionThe steel recycling factories in Thailand 50oC o 0.1 0.14 the rate constant (k1) of -1lead and chromium-1 generate a by-product called electric arc furnace o andfound Cr. to At be t 1,0.0869temperature min and40 C0.0586 (313.15K), min The steel recycling factories in Thailand 60 C -1 -1 were found to be 0.0825 min and 0.0276 mino dust (EAF dust). It is mainly ZnFe2O4 and 0.08 0.12 100 rpm the rate constant (k1) of lead and chromium generate a by-product called electric arc furnace respectively. For the t3, temperature-1 o 60 C-1 500 rpm respectively.were found toAt be t2 ,0.0825temperature min and 50 0.0276C (323.15K), min dustZnO. (EAF X -raydust). fluorescence It is mainly analysis ZnFe2O 4confirmedand 0.06 0.1 o 900 rpm therespectively.(333.15K), rate constant the At ratet 2(k, temperature2 )constant were found (k503) C ofto (323.15K), belead 0.0869 and ZnO.the chemicalX-ray fluorescence composition analysis of EAF confirmed dust of 32.16 0.04 0.08 -1 -1 -1 minthechromium rateand constant 0.0586 were min(kfound2) wererespectively. to found be 0.0937to be For 0.0869 minthe t 3, thewt% chemical zinc compositionand 31.68 wt% of EAF iron. dust The of 32.16 EAF dust Cr (ppm) concentration Cr -1 o -1 0.02 0.06 temperaturemin and 0.0586 60 C -1min(333.15K),respectively. the rate For constant the t3, wt%could zinc be and recycled 31.68 wt% instead iron. of Thethe directEAF dust disposal temperatureand 0.0801 60minoC (333.15K), respectively. the rateFrom constant Table could be recycled instead of the direct disposal 0 0.04 (k3) of lead and chromium were found to be into landfill. However, ZnFe2O4 the main 0 5 10 15 20 25 30 35 -1 -1 Cr (ppm) concentration Cr (k3,3 )it of was lead clearlyand chromium seen that were rate found constant to be into landfill. However, ZnFe2O4 the main Time (minutes) 0.02 0.0937 min -1 and 0.0801 min-1 respectively. chemical source of zinc in the EAF dust, is From0.0937increasing Table min 3,whenand it was0.0801 increase clearly min seenrespectively.temperature that rate chemicaldifficult source to transform of zinc ininto the ZnO EAF because dust, is of its 0 From Table 3, it was clearly seen that rate difficult to transform into ZnO because of its Figure 7 Residual Cr concentration as a function of 0 5 10 15 20 25 30 35 constant increasing when increase temperature stability complex compound. A reducing agent Time (minutes) constantbecause inatcreasing high temperature when increase the temperature activation stability complex compound. A reducing agent time for various temperature becausebecause atat highhigh temperaturetemperature thethe activationactivation waswas employed employed to decrease to decrease the energy the energy consumption consumption energyenergy (E (Ea)a ) isis declined.declined. However, the the authors authors in the calcining process. Calcium oxide (CaO) 3.2.3 Stirring Speed FigureFigure 9 Residual9 Residual Cr concentration Cr concentration as a function as ofa energy (Ea) is declined. However, the authors in the calcining process. Calcium oxide (CaO) time for various stirring speed suggestedsuggestedsuggested additionaladditionaladditional batchbatch experimentsexperiments of ofof waswas combined combined with with EAF EAF dust dustat a at1:2 a molar1:2 molar function of time for various stirring speed o To investigate the effect of stirring speed, cementationcementationcementation between between between 11 to 101 minutestominutes 10 minutesfor for accuracy accuracy for ratioratio and and then then sintered sintered at 700 at o700C forC 2 for hours. 2 hours. a Zn/Pb ratio of 3.0 was employed and 3.3 Cementation kinetics cementationcementation kinetic kinetic andand mechanism. TheThe calcined calcined EAF EAF dust, dust, with witha high a levelhigh level o 3.3 Cementation kinetics accuracy cementation kinetic and mechanism. a temperature at 60 C. The stirring speed of ofZnO, ZnO, was was then then leached leached by HCl. by HCl. The optimumThe optimum has little effect on the cementation kinetics for The The rate rateof reaction of reaction between between heavy metalsheavy 4 4 4040oCoC conditionsconditions were were found found to be;to 0.5Mbe; 0.5M HCl, HCl, the Pb, but an increasing in speed increases and more noble metals has been investigated in 3.53.5 o o o o metals and more noble metals has been 5050C C thetheS/LS/L ratio ratio of 1/10,of 1/10, tem peraturetemperature at 60 atC, 60 andC, and o the rate of removal of the Cr. Theoretically, various studies [12-14]. 3 6060CoC 3 stirringstirring speed speed of 900of 900 rpm rpm for 20for minutes. 20 minutes. The The investigatedHowever, in side various reaction studieswith the presence[12-14]. increasing stirring speed from 100 rpm to 900 2.5 solid residue after extraction was found to be of oxygen in the solution was not considered 2.5 solid residue after extraction was found to be rpm should increase the cementation rate because However, side reaction with the presence of 2 a potential source of iron. The concentration of 2 a potential source of iron. The concentration of of at higher speed there would be an increase in for this study. Thus, in this work, the following ln [Pb] ln [Pb] 1.5 lead and chromium after leaching at optimum oxygen in the solution was not considered for 1.5 lead and chromium after leaching at optimum molecule collisions. As seen in Figure 8 and heterogeneous first-order rate equation was conditions was 40.48 ppm and 0.12 ppm 1 conditions was 40.48 ppm and 0.12 ppm Figure 9, the concentration of Pb and Cr could appliedthis study. to calculate Thus, in the this rate work, constant. the following 1 respectively. Zinc cementation was applied to 0.5 respectively. Zinc cementation was applied to be closely reduced below 2 ppm. 0.5 reduce the impurities in the aqueous solution heterogeneousln [A] first-order – ln [A0] =rate -kt equation(1) was 0 Figure 8 and Figure 9 show at 500 rpm 0 10 20 30 40 reduce the impurities in the aqueous solution Where A is the concentration of lead and 0 prior to the electrowinning process. The optimum give the best result of Pb and Cr cementation. applied to calculate the rate constant. 0 10 Time (minutes)20 30 40 prior to the electrowinning process. The optimum chromium at time t. Time (minutes) conditions for cementation of the acidic leaching The results were compared to other investigations conditions for cementation of the acidic leaching ln [A] – ln [A0] = -kt (1) FigureFigure 10 The 10 relationship The relationship between ln[Pb] between and time solutions were found to be; Zn/Pb stoichiometric o [12,13]. Theory states that when stirrer was The rate constant (k) of the reaction was Figure 10 The relationship between ln[Pb] and time ratiosolutions of 3.0, weretemperature found toat be;60 C,Zn/Pb and stoichiometric500 rpm Where A is the concentration of lead and o rotated at very high speed it could increase the determined by the slope of the graph between ln[Pb] and time stirringratio rate of 3.0,for 10 temperature minutes operation. at 60 TheC, andleachant 500 rpm dissolution of the oxygen gas into the solution. the relationship chromium of ln[concentration]at time t. and time. 0 40oC performedstirring rate under for 10the minutes optimal operation. conditions The was leachant 0 The side reaction between metals and oxygen From the Figure 10 and Figure 11, the results -1 50oC 40oC sufficientperformed for reducingunder the lead optimal and chromium conditions to was The rate constant (k) of the reaction 60oC -1 50oC be 1.54 ppm and 0.007 ppm respectively. -2 sufficient for reducing lead and chromium to was determined by the slope of the graph 60oC Approximatelybe 1.54 ppm 95% and of 0.007lead andppm chromium respectively. -2 -3 were removed from the aqueous solution.
ln [Cr] Approximately 95% of lead and chromium between the relationship of ln[concentration] The zinc-rich solution after zinc cementation -3 -4 were removed from the aqueous solution. and time. From the Figure 10 and Figure 11, ln [Cr] is expectedThe zinc to-rich be suitable solution for after further zinc refining cementation to -4 -5 produce metallic zinc for the next process. the results show the cementation rate constant is expected to be suitable for further refining to o -5 -6 (k) of Pb and Cr. At t , temperature 40 C 0 10 20 30 40 produce metallic zinc for the next process. 1 Time (minutes) 5. Acknowledgments -6 The authors would like to thanks the (313.15K), the rate constant (k1) of lead and 0 10 20 30 40 Figure 11 The relationship between ln[Cr] and time -1 Time (minutes) Faculty5. Acknowledgments of Engineering, Kasetsart University chromium were found to be 0.0825 min and for the financialThe authors supported would throughout like this to research. thanks the -1 Figure 11 The relationship between ln[Cr] and time 0.0276 min respectively. At t2, temperature TableFigure 3 Cementation 11 The relationship rate constant, between k, as a functionln[Cr] ThanksFaculty to severalof Engineering, steel-making Kasetsart companies University in o Thailandfor the financialfor providing supported the ele throughoutctric arc furnace this research. 50 C (323.15K), the rate constant (k2) were of temperature and time Table 3 Cementation rate constant, k, as a function dustThanks sample to inseveral the research. steel-makingThanks, companies is also in extended to Dr.Greg Heness for the valuable of temperature Rate Constant, k, min-1 Thailand for providing the electric arc furnace Elements 40°C 50°C 60°C comments.dust sample Lastly, in thankthe research. you the DepartmentThanks, is also of Materials Engineering and Scientific 313.15KRate Constant,323.15K k,333.15K min-1 extended to Dr.Greg Heness for the valuable Pb 0.0825 0.0869 0.0937 Equipment and Research Division, Kasetsart Elements 40°C 50°C 60°C comments. Lastly, thank you the Department Cr 0.0276 0.0586 0.0801 Universityof Materials for laboratoryEngineering and andequipment Scientific 313.15K 323.15K 333.15K supported. Pb 0.0825 0.0869 0.0937 Equipment and Research Division, Kasetsart Cr 0.0276 0.0586 0.0801 University for laboratory and equipment supported. show the cementation rate constant (k) of Pb 4. Conclusion o and Cr. At t1, temperature 40 C (313.15K), The steel recycling factories in Thailand the rate constant (k1) of lead and chromium generate a by-product called electric arc furnace -1 -1 were found to be 0.0825 min and 0.0276 min dust (EAF dust). It is mainly ZnFe2O4 and o respectively. At t2, temperature 50 C (323.15K), ZnO. X-ray fluorescence analysis confirmed the rate constant (k2) were found to be 0.0869 the chemical composition of EAF dust of 32.16 -1 -1 min and 0.0586 min respectively. For the t3, wt% zinc and 31.68 wt% iron. The EAF dust temperature 60oC (333.15K), the rate constant could be recycled instead of the direct disposal (k3) of lead and chromium were found to be into landfill. However, ZnFe2O4 the main 0.0937 min-1 and 0.0801 min-1 respectively. chemical source of zinc in the EAF dust, is From Table 3, it was clearly seen that rate difficult to transform into ZnO because of its constant increasing when increase temperature stability complex compound. A reducing agent because at high temperature the activation was employed to decrease the energy consumption energy (Ea) is declined. However, the authors in the calcining process. Calcium oxide (CaO) suggested additional batch experiments of was combined with EAF dust at a 1:2 molar cementation between 1 to 10 minutes for accuracy ratio and then sintered at 700oC for 2 hours. cementation kinetic and mechanism. The calcined EAF dust, with a high level of ZnO, was then leached by HCl. The optimum 4 40oC conditions were found to be; 0.5M HCl, o 3.5 50oC the S/L ratio of 1/10, temperature at 60 C, and o 3 60 C stirring speed of 900 rpm for 20 minutes. The 2.5 solid residue after extraction was found to be
2 a potential source of iron. The concentration of ln [Pb] 1.5 lead and chromium after leaching at optimum
1 conditions was 40.48 ppm and 0.12 ppm
0.5 respectively. Zinc cementation was applied to reduce the impurities in the aqueous solution 0 0 10 20 30 40 prior to the electrowinning process. The optimum Time (minutes) conditions for cementation of the acidic leaching Figure 10 The relationship between ln[Pb] and time solutions were found to be; Zn/Pb stoichiometric ratio of 3.0, temperature at 60oC, and 500 rpm stirring rate for 10 minutes operation. The leachant 0 40oC performed under the optimal conditions was -1 50oC sufficient for reducing lead and chromium to 60oC be 1.54 ppm and 0.007 ppm respectively. -2 Approximately 95% of lead and chromium -3 were removed from the aqueous solution. ln [Cr]
-4 The zinc-rich solution after zinc cementation is expected to be suitable for further refining to -5 produce metallic zinc for the next process.
-6 0 10 Zinc 20Cementation30 of Heavy40 Metals5. fromAcknowledgments Electric Arc Furnace Dust Time (minutes) 31 Recycling Process Extracted by TheHydrochloric authors would Acid Solutionlike to thanks the Figure 11 The relationship between ln[Cr] and time Faculty of Engineering, Kasetsart University for the financial supported throughout this research. TableTable 33 Cementation Cementation rate rate constant, constant, k, as a k,function as a concentrationThanks to severalof lead steel and-making chromium companies after in of temperature Thailand for providing the electric arc furnace function of temperature leachingdust sampleat optimum in the research.conditionsThanks, was 40.48 is also Rate Constant, k, min-1 ppmextended and to0.12 Dr.Greg ppm Henessrespectively. for the valuableZinc Elements 40°C 50°C 60°C cementationcomments. wasLastly, appliedthank youto thereduce Department the 313.15K 323.15K 333.15K of Materials Engineering and Scientific Pb 0.0825 0.0869 0.0937 impuritiesEquipment in theand aqueousResearch solutionDivision, prior Kasetsart to Cr 0.0276 0.0586 0.0801 the Universityelectrowinning for laboratoryprocess. Theand optimumequipment supported. 4. Conclusion conditions for cementation of the acidic leaching solutions were found to be; Zn/Pb The steel recycling factories in Thai- stoichiometric ratio of 3.0, temperature at o land generate a by-product called electric 60 C, and 500 rpm stirring rate for 10 minutes arc furnace dust (EAF dust). It is mainly operation. The leachant performed under the ZnFe O and ZnO. X-ray fluorescence analysis optimal conditions was sufficient for reducing 2 4 lead and chromium to be 1.54 ppm and confirmed the chemical composition of EAF 0.007 ppm respectively. Approximately 95% dust of 32.16 wt% zinc and 31.68 wt% iron. of lead and chromium were removed from The EAF dust could be recycled instead the aqueous solution. The zinc-rich solution of the direct disposal into landfill. However, after zinc cementation is expected to
ZnFe2O4 the main chemical source of zinc be suitable for further refining to produce in the EAF dust, is difficult to transform metallic zinc for the next process. into ZnO because of its stability complex 5. Acknowledgments compound. A reducing agent was employed The authors would like to thanks the to decrease the energy consumption in the Faculty of Engineering, Kasetsart University calcining process. Calcium oxide (CaO) was for the financial supported throughout combined with EAF dust at a 1:2 molar ratio and this research. Thanks to several steel-making o then sintered at 700 C for 2 hours. companies in Thailand for providing the The calcined EAF dust, with a high electric arc furnace dust sample in the level of ZnO, was then leached by HCl. The research. Thanks, is also extended to Dr.Greg optimum conditions were found to be; 0.5M Heness for the valuable comments. Lastly, HCl, the S/L ratio of 1/10, temperature at thank you the Department of Materials 60oC, and stirring speed of 900 rpm for 20 Engineering and Scientific Equipment and minutes. The solid residue after extraction was Research Division, Kasetsart University found to be a potential source of iron. The for laboratory and equipment supported. 32 วิศวกรรมสาร มก.
6. References [8] Sriyowong P. (2013). Electric arc furnace dust treatment by calcium oxides [1] Dutra A.J.B., Paiva P.R.P. and Ta- from lime. Bachelor’s degree Thesis, Kaset- vares L.M. (2006). Alkaline Leaching of Zinc sart University, Thailand. from Electric Arc Furnace Steel Dust. Miner- [9] Polsilapa S., Jaithakul P. and Gul- als Engineering, 19(5): 478-485. rueang T. (2017). Zinc Recovery from Electric [2] Salihoglu G. and V. Pinarli (2008). Arc Furnace Dust Using Eggshell. Interna- Steel Foundry Electric Arc Furnace Dust tional Journal of Advances in Science Engi- Management: Stabilization by Using Lime neering and Technology, 5(4), Special Issue and Portland Cement. Journal of Hazardous Part 3: 1-4. Materials, 153(3): 1110-1116. [10] Younesi S., H. Alimadadi, E.K. [3] Lee J., Lin C. and Chen Alamdari, and S. Marashi (2006). Kinetic H. (2001). Carbothermal Reduction of Mechanisms of Cementation of Cadmium Ions by Zinc Powder from Sulphate Solutions. Zinc Ferrite. Metallurgical and materials Hydrometallurgy, 84(3-4): 155-164. transactions B, 32(6): 1033-1040. [11] Walton R. (2016). Zinc Cementa- [4] Orhan G. (2005). Leaching and tion, eds. Gold Ore Processing (Second Edi- Cementation of Heavy Metals from Electric tion). Elsevier, 553-560. Arc Furnace Dust in Alkaline Medium. [12] Lamya R.M. and Lorenzen L. Hydrometallurgy, 78(3): 236-245. (2005). A Study of Factors Influencing the [5] Langová Š., J. Léko, and D. Kinetics of Copper Cementation During At- Matýsek (2009). Selective Leaching of Zinc mospheric Leaching of Converter Matte. from Zinc Ferrite with Hydrochloric Acid. Hy- Journal of Southern African Institute of Min- drometallurgy, 95(3): 179-182. ing and Metallurgy, 105(1): 21-27. [6] Polsilapa S., Khamsrisaphap P. [13] Nadkarni R.M. and Wadsworth and Wangyao P. (2015). Electric Arc Furnace M.E. (1967). A kinetics study of copper pre- cipitation on iron: part II. Transactions of the Dust Treatment Process by Iron Powder. Key Metallurgical Society of American Institute of Engineering Materials, 656-657: 428-433. Mining, Metallurgical, and Petroleum Engi- [7] Polsilapa S., Intakuean P. and neers, 239: 1066-1074. Promboopha A. (2015). The Decomposition [14] J. Brent Hiskey and Jaeheon of Zinc Ferrite in Electric Arc Furnace Dust Lee (2003). Kinetics of gold cemen- by Carbon. Key Engineering Materials, 658: tation on copper in ammoniacal thiosul- 156-160. fate solutions. Hydrometallurgy, 69: 45-56.