Study On Solvent Extraction Of Precious Metals From Electronic Waste With New Extractants

Precious metals has been widely used in industrial circle,such as aerospace,national defense,chemical engineering,electronics and automotive,for its unique and excellent performance,which known as "vitamin of modern industry".With the rapid development of advanced technology,the demand for precious metals is increasing,while the electronic waste production has also increased dramatically.Electronic waste contains a variety of high-grade precious metal element,therefore,the recovery of precious metals from electronic waste has great economic importance and environmental significance.Solvent extraction has attracted widespread attention in field of precious metals recycling from e-waste,for its good selectivity,high metal recovery,low cost,extractants can be recycled and so on.Extractant is a major limiting factor for solvent extraction.Traditional extractant has bad acid resistance,low extraction capacity,hard stripping and other shortcomings,While amide extractant shows significant advantages in the above aspects,and can be completely incinerated with no secondary pollution.So amide extractant shows great application prospects in e-waste recycling.In our study,three new amide extractants have been synthesized and characterized,and their extraction properties of precious metals have been disused in detail.The main work is as follows:?1?Three new amide extractants N,N'-dimethyl-N,N'-didecyl-3-pentanediamide?MDDGA?,N,N'-dimethyl-N,N'-didecyl-3-thiopentanediamide?MDTDGA?,and N,N'-dimethyl-N,N'-diphenyl-3-thiopentanediamide?DMDPhTDGA?were synthesized through N-alkylated and N-acylation reaction,and were characterized by infrared spectroscopy.The synthesis cost of three extractants have been simply accounted,they are 9.45RMB/gMDDGA,5.81 RMB/gMDTDGA,2.54RMB/gDMDPhTDGA,respectively.?2?The extractability of Au???,Pd???,Pt???and Cu???using MDDGA diluted with 80vol%n-dodecane-20vol%2-ethylhexanol from hydrochloric acid was investigated.The maximum extraction efficiencies of four metal ions are 99.60%,6.72%,12.71%and 0.54%,respectively,when hydrochloric acid concentration is under 3mol/L.It indicates that MDDGA can separate Au???from a mixture solution containing Pd???,Pt???and Cu???.The research emphasis was the extraction performance of Au???with MDDGA in hydrochloric acid under 3mol/L.Several conclusions were obtained.The extraction equilibrium time is 30min.The extraction distribution ratio D increases with the increase of HCl concentration,H+ concentration,Cl-concentration and MDDGA concentration.The experiment proves that the extraction of Au???with MDDGA in low hydrochloric acid system is ion-association mechanism,and the extracted complex is?MDDGAH+?AuCl4-.?3?The extractability of Au???,Pd???,Pt???and Cu???using MDTDGA diluted with chloroform from hydrochloric acid was investigated.The maximum extraction efficiency of four metal ions are 99.87%,93.77%,10.03%and 1.62%respectively.The sequence of extraction capacity for four metal ions with MDTDGA is Au???>Pd???>>Pt???>Cu???.The research emphasis was the extraction performance of Au???and Pd???with MDTDGA in hydrochloric acid at 0-3M.It found that the extraction distribution ratio D increases with the increase of MDTDGA concentration,but decreases with the increase of HCl concentration and Cl-concentration,and is not influenced by H+ concentration,which indicates that the extraction of Au???and Pd???with MDTDGA in low hydrochloric acid system is coordination substitution mechanism,one Au???or Pd???coordinates with two extractant molecules,and the extracted complexes are MDTDGA2AuCl3 and MDTDGA₂ PdCl₂.?4?The extractability of Au???,Pd???,Pt???and Cu???using DMDPhTDGA diluted with chloroform from hydrochloric acid was investigated.The maximum extraction efficiency of four metal ions are 99.90%?98.91%?1.31%?1.20%,respectively.It shows that Au???is almost completely extracted,and the following is Pd???,but Pt???and Cu???are hardly extracted.The research emphasis was the extraction performance of Au???and Pd???with DMDPhTDGA in hydrochloric acid at 0-3M.The extractability trends of Au???and Pd???with DMDPhTDGA on HCl concentration,H+ concentration,Cl-concentration and extractant concentration are similar to MDTDGA,which evidences that the extraction of Au???and Pd???with DMDPhTDGA in low hydrochloric acid system is coordination substitution mechanism.One Au???coordinates with two extractant molecules,and one Pd???ion coordinates with one extractant molecules.The extracted complexes areQ DMDPhTDGA₂AuCl₃ and DMDPhTDGAPdCl₂.