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Nghiên cứu ảnh hưởng của nhiệt độ đến quá trình hòa tách vàng từ rác thải điện từ sử dụng thiosulfate trong môi trường ammoniac với xúc tác đông (II)

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Nghiên cứu ảnh hưởng của nhiệt độ đến quá trình hòa tách vàng từ rác thải điện từ sử dụng thiosulfate trong môi trường ammoniac với xúc tác đông (II)

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Nhằm thúc đẩy phát triển công nghệ thân thiện môi trường để tái chế thu hồi kim loại quý từ chất thái điện tử, quá trình hòa tách vàng bằng thiosulfate đã được quan tâm trong vài năm gần đây. Nghiên cứu này khảo sát sự ảnh hưởng của nhiệt độ đến động học của quá trình hòa tách vàng và quá trình khử không mong muốn của đồng (II) bởi thiosulfate trong điều kiện thí nghiệm 10 mM CuSO4, 0,1MNa2S2O3 và 0.45M NH3/NH4+. Tốc độ hòa tách của vàng được xác định trong điều kiện nồng độ dung dịch không đổi sử dụng phương pháp tốc độ ban đầu, bằng cách đo sự thay đổi nồng độ theo thời gian trong vòng vài phút. Năng lượng hoạt hóa của phản ứng trong khoảng nhiệt độ từ 20 - 50 độ C được tính là 78.6 kJmof. Động học quá trình hòa tách vàng do phản ứng hóa học cho phối.

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Nội dung Text: Nghiên cứu ảnh hưởng của nhiệt độ đến quá trình hòa tách vàng từ rác thải điện từ sử dụng thiosulfate trong môi trường ammoniac với xúc tác đông (II)

STUDY ON EFFECT OF TEMPER.\TURE ON GOLD LEACHING FROM<br /> ELECTRONIC SCRAPS USING THIOSULPHATE WITH COPPER(II) CATALYST<br /> IN AMMONIA MEDIA<br /> NGHIEN CUU ANH HUONG CUA NHIET DO DEN QUA TRJNH HOA TACH VANG TU" RAC<br /> THAI DIEN TU" SU" DUNG THIOSULFATE TRONG MOI TRUONG AMMONIAC VCDl XUC<br /> TAC D6NG(I1)<br /> <br /> <br /> Ha Vinh Hung ', Huynh Trung Hai', Ngo Thi Nga ', Jae-chun Lee \ Jinki Jeong'<br /> Hanoi University of Set 'nee and Technology (HUST)<br /> Korea Institute ofGeoscienc - and Mineral Resources (KJGAM)<br /> <br /> ABSTRACT<br /> In order to develop an environmentally friendly technique for recovery of precious metals from<br /> electronic scrap, thiosulfate leaching of gold has focused in recent years. This study investigates the<br /> effect of temperature on the gold leaching kinetics and the undesirable homogeneous copper(ll)<br /> reduction by thiosulfate under experimental conditions of 10 mM CUSO4, 0.1 M Na2S203 and 0.45M<br /> NH3/NH4* The leaching rate of gold Is determined at essentially constant solution concentrations<br /> using the method of initial rates, which measures concentration changes in real time within minutes.<br /> The activation energy of the leaching reaction in the temperature range 20 - 50°C was found to be<br /> 78.6 kJ.mof' The gold leaching kinetics were found to be chemically controlled.<br /> <br /> TOM T.\T<br /> Nhim thuc diy phit triin cdng nghe thin thien mdi trwding di tii chi thu hdi klm loai quy tir<br /> chit thii dien tir, qui trinh hda tich ving bing thiosulfate da dwac quan tim trong vil nam gin day<br /> Nghien ciru niy khio sit sw inh hwdng cua nhiet do din ddng hoc cua qua trinh hda tich ving vi<br /> qui trinh khir khdng mong mudn ciia ddng (II) bdi thiosulfate trong diiu kien thi nghiem 10 mM<br /> CuSOi, 0 1M /VajSsOs vi 0.45M NH3/NH4* Tdc do hda tich ciia ving dwac xic dinh trong diiu kien<br /> ndng dd dung dich khdng ddi sir diing phwong phip tdc dd ban diu, bing cich do sw thay ddi ndng<br /> dd theo th&i gian trong vdng vii phut Nang lwang hoat hda cua phin irng trong khoing nhiet do tir 20<br /> - 50°C dwac tinh la 78.6 kJmof\ Ddng hoc qui trinh hda tich ving do phin irng hda hoc chi phdi.<br /> <br /> <br /> I. INTRODUCTION The leaching of gold with thiosulfate<br /> Nowadays, waste electric and electronic solutions has been extensively studied as an<br /> equipment, or electronic waste, has been taken altemative method for the traditional<br /> into consideration not only bv the government cvanidation technology [2]. It is known that in<br /> but also by the public due to their hazardous the presence of ammonia and copper ions, gold<br /> nialerial contents. CurrentK. the main options can be readily brought into solution by the<br /> for the treatment of electronic waste are formation of a gold thiosulfate complex, as<br /> involved in reuse, remanufacturing, and shown in Eq. (1).<br /> recycling, as well as incineration & landfilling.<br /> (iold metal has a wide application in the Au - Cu(NH,)4 '" + 5S2O,-" -^ Au(S,O.0:"'"<br /> manufacture of electronic appliances, serving as -Cu(S:05),' +4NH, (1)<br /> contact material due to their high chemical<br /> The thiosulphate leaching system is<br /> stabilitv and their good conducting properties.<br /> complicated by the homogeneous reduction of<br /> Ihe detailed literatuie siirvev of J irang Cui et<br /> Cu(ll) by thiosulphate according to the<br /> al. on value distributions for different electronic<br /> simplified overall reaction, Eq. (2) [3].<br /> waste samples showed that the major economic<br /> driver for recvcling of electronic waste is from Cu(NH04"'-8S:O/ - ^ 2CU(S203)3''<br /> the recovery of gold metal [I].<br /> - S4O,," 8NH-, (2)<br /> JOI RN \ L OF SCIENCE & TECHNOLOGV<br /> <br /> In the absence of oxvgen the products titration, a certain amount of acetic acid (10%<br /> from this reaction are cuprous complex and solution) was added prior to the titration uiih<br /> tetrathionate [4]; therefore, the reaction not only the indicator \ i t e x . The concentration of the<br /> reduces the cupric ion concentration required cupric ammonia complex was detennined ai<br /> for leaching but also destrovs thiosulfate. 608 nm wavelength using L"V-\is spectro-<br /> photometry (Shimadzu). The solution<br /> The aim of this studv is application the<br /> absorbance was recorded at regular time<br /> technologv for thiosulphate leaching of gold to<br /> intervals via a computer. The temperature. pH<br /> recover gold in scrap from electronic industry<br /> and redox potential of the solution were<br /> in condition of optimal temperature. This is a<br /> monitored during leaching all time. Surface of<br /> new approach. important from both<br /> scrap samples before and after leaching were<br /> environmental and economical points of view.<br /> analv'zed using a Hitachi Jeol scanning electron<br /> II. MATERIAL AND METHODS microscope, combined with an X-ray analyzer<br /> [scanning electron microscopv-energ)'<br /> Material. \\ aste scrap samples were<br /> dispersive spectroscopy (SEM-EDS)].<br /> obtained from mobile phone factorv in Korea,<br /> which the average content of gold of 440 g't. III. RESUUTS AND DISSCUTION<br /> Contact surface of gold metal of each scrap<br /> 3.1 SEM-EDS analysis: formation of sample<br /> plate is 486 mm"" Analv tical grade ammonium<br /> layers<br /> thiosulphate. ammonium sulphate, ammonia<br /> solution (25%) and cupric sulphate were used in Morphologv studies of the dilTerenl<br /> the experiments. The leach solution was composition of the sample section were carried<br /> prepared bv dissolving the proper chemicals in out bv means of SEM. Its image is showed in<br /> deionized water to the required concentration. Fig. 1 shows that there are four lavers from<br /> In each instance, the aqueous ammonia was outside to inside, including: gold, nickel, copper<br /> mixed with the eopper(ll) sulphate prior to and plastic. Therefore, other metals in sample<br /> addition to the ammonium thiosulfate (nickel, copper) were not contacted with the<br /> containing solution, and finallv the pH of the solution so did not affect gold leaching.<br /> solution was adjusted 9 - 1 0 also with aqueous<br /> ammonia.<br /> Methods Leaching experiments were<br /> carried out in a 0.5-L Pvrex glass reactor using<br /> a magnetic stirrer at a rotating speed of 400<br /> rpm. Each test was used 400 mL leaching<br /> solution and 10 plates of scrap sample. The<br /> scrap samples were suspended in the upper part<br /> of the leaching reactor with a nvlon thread,<br /> ensuring no contact w ith the reactor wall during<br /> leaching. 1 he temperature was controlled with a<br /> thennoslalie water bath at _-0.5 C of the set<br /> values. During the experiment, the solution was<br /> deaerated with high-puritv nitrogen. Samples<br /> were taken continuouslv at certain intervals<br /> during a total retention lime of 10 minutes.<br /> Fig. 1. SEM image of .sample section helnrc<br /> fhe gold concentration in the leach leaching.<br /> solutions was detennined by ..\.\S (Perkin Elmer<br /> The EDS analysis resuls also indicated<br /> \ \4iiiii. In each lest, the final residue was dried that the gold layer outside was of over 90°o<br /> and leached bv aqua regia to analvze for gold. puritv.<br /> The thiosulphate concentration was determined<br /> by iodomelrie method. In order lo eliminate the<br /> cllcci ol the cupric ammonia complex on iodine<br /> jwi,iv>.ALur SCIENCE & TECHNOLOGY * No.82A-201l<br /> <br /> 3.2 Dissolution of gold In thiosulphate reduction rate is negligible reduced with 10<br /> system solution minutes required for the copper(ll)<br /> concentration to decrease from 10 to 9 mM; in<br /> The changes in leaching performance of<br /> comparison, the copper(Il) concentration is<br /> gold and cupric ammonia complex<br /> reduced to 5 mM in 1 minute in temperature at<br /> concentration with time under various<br /> 50°C. This explains the cause of the leaching<br /> experimental conditions are illustrated in Fig. 2<br /> performance of gold is 91% only in this case.<br /> and Fig. 3, respectively. It is evident from Fig.<br /> 2 that temperature has a significant effect on the The energy dispersive X-ray analysis<br /> reaction rate of gold leaching (which is (EDX) was cartied out using a SEM-EDS for<br /> expected for a chemically controlled reaction). qualitative analysis of surfaces before and after<br /> At 20°C, the reaction rate is very low, less than leaching. Its spectrum (Fig. 4) shows that gold<br /> half of gold is leached in 5 minutes. While is not detected in sample affter leaching.<br /> almost all the gold being extracted in 2 minutes<br /> at above 40°C. It is worth noting that the 3.3 The activation energy of gold leaching<br /> mixed potential of gold leaching at steady reaction<br /> state was found to decrease with increasing The general form of the initial rate equation<br /> temperature. for reaction (1) can be expressed as:<br /> Beside, the temperature also has r = i[NH3r[S203'T[Cu(NH3)4' (3)<br /> dramatically affected the kinetics of the<br /> where k is the rate constant, the k value is<br /> copper(II) reduction by thiosulfate during the<br /> dependent on temperature and pressure; and a.<br /> thiosulfate leaching of gold. The results in Fig.<br /> b and c are reaction orders with respect to<br /> 3 shows that the rate of copper(ll) reduction<br /> ammonia, thiosulfate and cupric ammine<br /> by thiosulphate is increased with increasing<br /> complexes, respectively. At chemical initial<br /> temperature. For instance, the initial reaction<br /> concentrations of constant, Eq. (3) can be<br /> rate at 40°C is 3.2 times higher than the initial<br /> written as:<br /> rate at SCC and 3.9 times lower than the<br /> innitial rate at 50°C. However, it can be seen<br /> from Fig. 3 that at 20°C, the copper(Il)<br /> <br /> <br /> <br /> <br /> 4 6<br /> <br /> 0 1 2 3 4 5 6 Time (min)<br /> <br /> Time (min)<br /> <br /> Fig. 2. The effect of temperature on gold Fig. 3. Changes in gold concentration with time<br /> leaching. Experimental conditions: 10 mM during its leaching under various condition of<br /> CiiSOj. OlMXa.S.'O.i, 0.45.M Mf. XH4 temperature. Experimental condition: 10 mM<br /> CiiSOe. O.l.MXayS^Oe. 045MNHeNH4<br /> JOL RNAL OF SCIENCE & TECHNOLOGV *<br /> <br /> <br /> <br /> <br /> •wjd 4<br /> <br /> <br /> <br /> \y*.' i;<br /> <br /> >ii<br /> <br /> <br /> 1 fl<br /> U ^yiri . -2 0<br /> 1 u<br /> 1600<br /> t Sl \ is<br /> I2KI 1 < s "1 1<br />
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