| As the consumption of precious metals is increasing year by year and the content in the earth’s crust is limited,the cost of mining precious metals from primary mines has become higher and higher due to the declining ore grade.Secondary resources(such as waste computer circuit boards,industrial organic synthesis catalysts,waste automobile exhaust catalysts,etc.)have huge reserves due to a wide range of sources,and the content of precious metals to be mined is much higher than the content of precious metals in primary mines.Therefore,the development of green and clean technologies that efficiently recover precious metals from secondary resources is also a general trend in the development of the mining industy.Because of the high toxicity,low extraction efficiency,difficulty of recovery,and the use of toxic and volatile organic solvents such as benzene,chloroform and kerosene as diluents,the large quantities of extractants used in traditional extraction technologies can no longer meet the needs of environmental protection.Therefore,it is the starting point of this thesis to explore the recovery technology of low toxicity,high recovery efficiency,good cycle performance,and good selectivity for precious metals in the complex environment where heteroions exist.Sulfur-containing extractant has a high affinity for precious metals due to its mercapto group,so it has the characteristics of high extraction efficiency,good selectivity and good recyclability when extracting precious metals.To this end,three sulfur-containing extractants were designed in this paper,and their performance in extracting and separating precious metals was studied.First,neutral 1-hexyl-3-methylimidazothione was synthesized,and its extraction behavior of Au(Ⅲ)in hydrochloric acid solution was studied.Condition optimization experiments were carried out for various factors affecting the extraction behavior of Au(Ⅲ),such as equilibrium shaking time,hydrochloric acid concentration,NaCl/NaBr concentration,1-hexyl-3-methylimidazolidone dosage,and extraction selectivity.The results show that 1-hexyl-3-methylimidazothione exhibits excellent extraction effect on Au(Ⅲ),and the extraction rate is less affected by external conditions;it exhibits an excellent effect in mixed metal solutions with many hetero ions.Au(Ⅲ)has high efficiency and selective extraction ability.Through Fourier Infrared Transform Spectroscopy,Equimolar Continuous Transformation and comparative experiments,it was determined that the extraction of Au(Ⅲ)with 1-hexyl-3-methylimidazolidone followed the coordination substitution mechanism,and it was proved that the S atom is the extraction point of action of the effect.After five rounds of extraction and stripping cycle experiments,the system can still achieve an extraction rate of 90%for Au(Ⅲ)in the water phase,which proves that the system has good cycle performance.Secondly,2-mercaptobenzimidazole,which is low-cost and widely sourced,was selected to study the performance of extracting and separating Pd(Ⅱ),Pt(Ⅳ),and Rh(Ⅲ)in hydrochloric acid solution.After optimizing the conditions for the individual metal ions,the optimal separation conditions for the three metals were determined,and the separation route were designed with two-step extraction experiment of metal ions by controlling the concentration of hydrochloric acid in the aqueous phase and the amount of 2-mercaptobenzimidazole in the organic phase.The results showed that the three metal ions were successfully separated after two-step extraction and stripping experiments,and the purity of Pd(Ⅱ),Pt(Ⅳ)and Rh(Ⅲ)could reach 91%,93%and 97%,respectively.At the same time,combined with Fourier infrared spectroscopy,ultraviolet-visible spectroscopy and comparative experiments,it is determined that under the best separation conditions,the extraction of Pd(Ⅱ)by 2-mercaptobenzimidazole follows the coordination substitution mechanism,and the extraction of Pt(Ⅳ)follows the ion association mechanism.Using an acidic thiourea solution with a concentration of 0.5 mol·L-1 can easily extract Pd(Ⅱ)and Pt(Ⅳ)from the loaded organic phase to achieve the enrichment of the three metals.Although 1-hexyl-3-methylimidazolethione and 2-mercaptobenzimidazole exhibit good extraction and separation capabilities for precious metal ions in the aqueous phase,they are dependent on organic solvents and the treatment process is more complicated.Therefore,exploring the non-solvated precious metal recovery process is the focus of the next work.For this reason,we synthesized(3-mercaptopropyl)trimethoxysilane functionalized magnetic ferroferric oxide nanoparticles,and tested their adsorption and separation performance of Au(Ⅲ),Pd(Ⅱ)and Pt(Ⅳ).Through the maximum loading experiment,it is determined that the maximum adsorption capacity of magnetic Fe3O4@SiO2-SH for Au(Ⅲ),Pd(Ⅱ)and Pt(Ⅳ)are 73.9 mg/g,33.486 mg/g and 1.3 mg/g,respectively.Then,the influence of various factors(initial metal ion concentration,hydrochloric acid concentration,NaCl concentration,etc.)in the water phase on the adsorption behavior of the three metal ions was investigated.The results show that the adsorption of three metal ions by Fe3O4@SiO2-SH is less affected by external factors.Since the adsorption capacity of the magnetic nanoparticles for Pt(Ⅳ)is far less than the adsorption capacity for Au(Ⅲ)and Pd(Ⅱ),the preferential separation of Pt(Ⅳ)from the solution in which the three metals are mixed can be realized.However,the similar adsorption behavior of Pd(Ⅱ)and Au(Ⅲ)makes it impossible to achieve their effective separation by controlling the conditions in the water phase.For this reason,we propose a scheme for pretreatment of the metal solution:before using magnetic nanoparticles to adsorb metal ions,an extractant is used to remove a metal ion.Finally,we chose cyanex272 as the pretreatment agent to selectively extract Au(Ⅲ).Its cycle performance has also been further studied.The results show that the adsorption rate of Au(Ⅲ)and Pd(Ⅱ)on the magnetic Fe3O4@SiO2-SH nanoparticles can still reach 90%after six rounds of cyclic stripping experiments,which proves that the sulfhydryl functionalized magnetic Fe3O4 nanoparticles particles have great application potential in adsorbing precious metals. |
PDF Full Text Request