Separation And Recovery Of Precious Metals From Waste Feed Containing Precious Metals With Solvent Extraction

Platinum group metals are used widely due to the particular properties. Since the nature resources in our country are limited, so the recovery from secondary resources becomes more and more important. As an advanced method of purifying and separating precious metals, solvent extraction is applied to retrieve rare metals. The key to the technology is to exploit new extractant and process.In this paper, the two kinds of sulfoxids, namely isooctyl benzothiazole sulfoxide(ASO) and sulfoxide MSO are synthesized. The synthetical method of MSO is improved, which has many advantages such as saving time, low cost, simple operation and higher purity of product. The yield of MSO reaches 88.88% and the content of sulphur in MSO is 10.40%.The performance of extracting palladium with ASO is studied. The effect factors such as diluent, [HC1], [H⁺] and [Cl^-] on the percentage extraction or distribution ratio are determined. The ammonia is used to strip the loaded organic phase. The composition of extraction complex is shown to be PdCl₂ · 2ASO by slope method. The extraction mechanism is neutral coordination and the equilibrium equation is achieved.The performance of extracting palladium with MSO is studied. The effect of the feed acidity on the equilibrium is significant. The result shows that the ammonia is a good stripping agent. Capacity of extracting palladium with 30%MSO is more than 13g · L^-1 .On the foundation, the performance of extracting platinum with MSO is studied and compared with that of palladium. The result indicates that the percentage extractions of palladium and platinum both increase with extractant concentration and [H⁺] increasing. [Cl] effects the percentage extraction of palladium but not that of platinum. So under high acidity, the co-extraction and separation of platinum and palladium will be realized by choosing suitable extractant concentration.Study of the performance of ASO and MSO extracting platinum and palladium showed the possibility of appliance of MSO in industry, so the feed containing platinum, palladium and rhodium is dealt by 30%MSO. Counter-current cascade stage test is simulated. The result indicates that sum recoveries and direct recoveries of platinum and palladium are both more than 100%, while the rhodium is leaved in the raffinate. The extraction and separation of platinum, palladium and rhodium are realized. So the pilot test was done.The pilot test of extracting platinum, palladium and rhodium from feed with 30%MSO was done. The result indicated that for the feed containing platinum and palladium, the percentage extraction and stripping of platinum and palladium are both over 99%. The ratio of palladium to platinum is only 0.0016 in stripping platinum solution. The ratio of platinum to palladium in stripping palladium solution is 0.0020. For the feed containing platinum and rhodium, the percentage extraction of platinum reaches 99% and the percentage stripping of platinum reaches 100%. The ratio of rhodium to palladium in the stripping platinum solution is 0.0002. Precious and base metals is separated with P204- The percentage extraction of copper is more than 99.5% and the percentage stripping was about 100%, but rhodium is not extracted under the test condition. So the new process which extracts and separates precious metals is gained. Comparing with traditional precipitation method, the extraction is shorter in process and period. In addition, there are some advantages such as simple operation, saving time and labor. The most important aspect is that the extractant MSO is high boiling point and non-toxic sulfoxide, so there is not special smell in operation ground and environment pollution is low.For the feed containing platinum and iridium, Firstly, it is pretreated, then, the cascade stage test is simulated. The direct recovery of platinum reaches 94.1% and sum recovery reaches 94.5%. The content of iridium in stripping platinum solution is 0.08%, so most of iridium is leaved in raffinate.The recovery of gold and copper from waste printed circuit board with H2O2-H2SO4 solution is studied. The influences of concentration and amount of sulfuric, solid-liquid ratio, the amount of hydrogen peroxide and reaction time on the reaction are investigated. Desquamating rate of gold reaches 98.75% and recovery of copper reaches 99.43%. The reagents are nontoxic, cheap and easily gained. The equipments are simple and it is convenient to operate. No toxicant is produced during the course of reaction. Reuse of precious resources is realized.Lewis cell is used to research kinetics of stripping gold loaded on DBC organic phase with sodium sulfite. With stirring speed of 400r ? min'1, stripping gold is confirmed the pseudo-first-order reaction. Stripping rate of gold is direct ratio to interfacial area and concentration of sodium sulfite and stripping rate increases with temperature increasing. The activation energy of reaction is 36.06kJ ?mol"1.It is thought that the reaction is interfacial chemical control process. The kinetics equation of sodium sulfite stripping gold is put forward.