Study On The Re-extraction Of Spent Auto-catalysts Leaching Residue By Chlorination

Automobile leaching residue is the residual slag leached from spent auto-catalysts by means of aqueous chlorination.The aqueous chlorination,because of the simple equipment,less investment,short payback period of it,has been used extensively as one of the most important methods recycling platinum group metal from spent auto-catalysts.While the disadvantage of this method is that the content of precious metals in the leaching residue could reach as high as 80--100g/t,so the leaching residue still has comprehensive economic value.The exploration of the residual mechanism of the platinum group metal,and the exploration of the extracting craft,they both have significant practical meanings in the development and utilization of the important platinum group metal resource.Basing on abundant data and analyzing the reasons noble metals remain in the leaching residue,the influences of the oxidizing roasting,reduction,and oxidizing roasting combined with reduction pretreatment on the leaching rate have been studied systematically in this thesis.The experiment results show that the organics and carbon deposition on the surface of the spent auto-catalysts could be removed after being pretreated with oxidation roasting,and also leading to a much higher leaching rate compared with the spent auto-catalysts without any pretreatment.The leaching rate of Pt,Pd,Rh in the spent auto-catalysts would reach 78.89%?19.37%?17.97%respectively after spent auto-catalysts being pretreated under the conditions of oxidation roasting at 200? for 3 hours.The reduction pretreatment could change the oxide of platinum group metals to elementary substance,which will be advantageous to improvement of the leaching rate of platinum group metals.Compared with the spent auto-catalysts without any pretreatment,the leaching rate of Pt,Pd in the spent auto-catalysts with reduction pretreatment have been increased by 5%?11%and to 69%?28%respectively.Composite pretreatment,oxidation roasting combined with reduction pretreatment,can remove the coat organics and carbon deposition over spent auto-catalysts.In the meantime,a portion of platinum group metal oxides wound be reduced,which is good for leaching.The leaching rate of Pt,Pd,Rh in the spent auto-catalysts would reach 72.23%?33.54%?15.00%respectively after spent auto-catalysts being pretreated under the conditions of oxidation roasting at 600? for 3 hours first,followed by reduction with sodium borohydride.