With the rapid development of the electronics industry, the number of printed circuit boards (PCBs) has also increased dramatically. Not recycling a large number of discarded PCBs will not only cause serious pollution to the environment, but also result in the waste of a lot of precious resources. The main purpose of recycling electronic waste is to recover the rare precious metals contained. Rare and precious metals play an important role in improving the performance of PCBs. Among rare precious metals, people pay the most attention to recycling gold; because in the past 30 years, a certain amount of gold has been used in the electronics industry. In the United States and Europe, the gold consumption for the electronics industry was 82 in 1968, t reached 127 in 1972, and t fell to 67 in 1975; t from 1978 to the present, the annual consumption of gold has remained stable at around 80t. For the recovery of gold in PCBs, the most commonly used chemical method is the chemical method. The main processes are: alkaline leaching (thiosulfate, cyanide) or acid leaching (nitric acid, aqua regia) for the treatment of gold-containing waste, so that Gold exists in the solution in the state of complex ions, and then, using solvent extraction, activated carbon adsorption, anion resin exchange and other methods, the gold is separated and enriched from the leaching solution. The author proposes to use a double aqueous phase extraction system to extract gold in acid leaching solution, which is one of the emerging methods in solvent extraction. The so-called double aqueous phase is a polymer or two polymers and a salt dissolved in the same solvent, when the concentration of the polymer or inorganic salt reaches a certain value, due to the polymer or between the polymer and the salt The incompatibility of the two will form two incompatible phases. The aqueous two phase system (ATPS) utilizes the phenomenon that the two aqueous phases are in phase and the difference in the partition coefficients of the substances to be separated between the two phases to achieve the purpose of separation and purification. The dual aqueous phase extraction technology has been widely used in the fields of biochemistry, cell biology, biochemical industry and food chemical industry, and has achieved many successful examples with broad industrial application prospects. Relatively double water is correspondingly used in the biological field, and this system is used in the distribution of metal ions less research. After Zvarova proposed the possibility of using this system to separate metal ions, the research on the distribution behavior of inorganic ions in the two-aqueous phase system was gradually developed. At present, the research on the separation of metal ions using this technology is quite active. The distribution behavior of gold () in the polyethylene glycol-ammonium sulfate two-phase aqueous system is studied, and the distribution of KAu (CN) 2 in the two aqueous phases is studied. law. 1 Test part 1.1 Test sample The pretreatment solution is to dismantle the waste printed circuit board first, separate the plastic and metal plates, and then mechanically break the metal plate. The broken particles are 70 200 mesh. At this time, the electronic waste contains more than 90% copper. Direct dissolution with aqua regia is not conducive to later extraction, so first remove most of the copper and other metals with nitric acid, and then dissolve the filtered filter residue with aqua regia, adjust the pH of the solution with hydrochloric acid = 1. Prepare a gold-containing solution with a mass concentration of 3 mg / L for the extraction test. 1. 2 Reagents and instrument reagents: PEG series, ammonium sulfate, nitric acid, hydrochloric acid, acetic acid, sodium acetate are all analytically pure. The test water is deionized water. The buffer solution was prepared according to document <8>. Instruments: AA320 atomic absorption spectrophotometer (Shanghai Analytical Instrument Factory); FD-97 oil-free air compressor (Fudan University Science and Education Instrument Factory); KY series hollow cathode lamp (Hebei Hengshui Ningqiang Light Source Company); YP600 electronic balance (Shanghai Second Balance Instrument Factory); pHS- 3TC acidity meter (Shanghai Tianda Instrument Co., Ltd.); constant temperature water bath. 1. 3 Test method Take 7ml of gold-containing solution in a 30ml graduated separatory funnel, add 15ml of PEG solution with a certain mass fraction, and then add 8ml of buffer solution to adjust the pH of the extraction system so that the final volume is 30m. l After shaking, add a certain amount of phase-separated salt ammonium sulfate, put it in a water bath at a constant temperature, and shake to extract 3min; after the solution phase separation is complete, separate the PEG phase and the brine phase to prepare a 3% HCl solution , Atomic absorption method was used to determine the mass concentration of gold in the brine phase and PEG phase, and the extraction rate was calculated. 1. 4 Experimental mechanism Au 3+ easily undergoes nucleophilic substitution reaction with halogen ions to form complexes. The main form of Au 3+ in the liquid to be extracted is AuCl 4-. The PEG phase after extraction of AuCl 4-was analyzed by ultraviolet-visible spectroscopy, and compared with the aqueous solution of AuCl 4-, it was found that the maximum absorption peak of AuCl 4-in the aqueous solution to be extracted appeared at a wavelength of 314 nm, while the maximum absorption of the PEG phase extract The peak is at a wavelength of 317nm, indicating that after extraction into the PEG phase, the morphology of Au 3+ has not changed, and still exists in the form of AuCl 4-. The structure of AuCl 4-does not match with the extractant and its structure remains unchanged. The extraction reaction involves H +. The ion with a small surface charge density is conducive to extraction. The extraction has the characteristics of ion-associated extraction. The extraction reaction includes: H + in the aqueous phase and a part of PEG through hydrogen bonding to generate a solvated cationic PEGH + (1) formula; PEGH + and AuCl 4-complex anions form electrostatically neutral ion pairs <(PEGH) + ( AuC l 4)->, extracted into the precipitated PEG phase (2) formula; Cl-competition into the PEG phase (3) formula. H + + PEG PEGH + (1) AuC l 4-+ (PEGH) + <(PEGH) + (AuCl 4)-> PEG phase (2) Cl-+ (PEGH) + <(PEGH) + Cl-> PEG Phase (3) According to equations (1) and (3), the extraction reaction can be expressed as: 2H + + 2PEG + AuCl 4-+ Cl-<(PEGH) + (AuCl 4)-> PEG phase + <(PEGH) + C l -> PEG phase 2 test results and discussion 2.1. Effect of pH on extraction rate At a temperature of 25, in a 30ml graduated separatory funnel, add 7ml of gold solution with a concentration of 3mg / L to be extracted, add 15ml of 30% PEG2000 solution, add 8ml of different buffer solvents to change the pH value of the extraction system, and finally add 6g of phase-salt ammonium sulfate (mass fraction of 20%) to investigate the effect of pH changes on the gold extraction rate. It can be seen that the extraction rate of gold increases as the pH value decreases; when pH = 1, the extraction rate reaches a maximum of 84.99%. The pH value continues to increase, and the extraction rate decreases instead, because PEG-(NH 4) The formation of 2 SO 4 double aqueous phase system is the result of salting out. The increase of the pH value of the solution weakens the salting out of (NH 4) 2 SO 4, which makes the phase separation difficult and reduces the extraction rate. In the gold extraction process, the pH value of the solution affects the formation of the association of gold ions and the extractant, the stability of the association, the surface charge, etc., thereby affecting the gold extraction rate. Therefore, pH is an important factor in the distribution of gold in the two-aqueous phase system, and it is relatively easy to control, so it has also become the main control condition for the extraction and separation of the two-aqueous phase. 2. 2 The effect of PEG mass fraction on extraction rate At 25 temperature, in a 30ml separatory funnel, add 7ml of gold solution with a mass concentration of 3mg / L, and add the mass fractions of 10%, 20%, 30%, 40% and 60% of PEG2000 solution 15m, l add 8m l pH = 1 buffer solvent, and finally add 6g of phase-salt ammonium sulfate (mass fraction 20%), to investigate the change of PEG mass fraction on gold extraction rate influences. It can be seen that in the case of a low PEG mass fraction (<10%), the gold extraction rate is less than 80%; after the PEG solution reaches a certain mass fraction (15%), the gold extraction rate reaches 84%. Continue to increase With a large PEG mass fraction, the extraction rate of gold is basically unchanged, resulting in a waste of PEG solution; at the same time, the phase separation time is increased, see details. Therefore, in this experiment, an extraction system with a PEG mass fraction of 15% was selected, that is, when the total extraction volume was 30 ml, 15 ml of 30% PEG2000 solution was added. Fruit Tools,Lemon Squeezer,Lemon Juice Squeezer,Pineapple Corer Xiongyang Household Co., Ltd , https://www.xyknives.com