沉金后液中金、铂、钯、碲的组态特征及其碲捕集稀贵金属机制

铜阳极泥沉金后液是回收铂族金属铂、钯的重要原料来源。根据铜阳极泥氯化浸出过程稀贵金属可能发生的电极反应,分析了沉金后液中金、铂、钯、碲的存在价态,通过热力学计算绘制了金、铂、钯、碲的多形态组分图,并研究了单一金、铂、钯体系碲捕贵金属机制。沉金后液中稀贵金属金、铂、钯和碲的价态分别为Au³⁺,Pt²⁺,Pt⁴⁺,Pd²⁺,Te⁴⁺;金、铂、钯在沉金后液中随氯离子浓度的改变,以多组态络合物形式存在,Au(Ⅲ)几乎全部以AuCl₄]-组态存在,Pt(Ⅱ),Pd(Ⅱ)分别主要以PtCl₄]₂-,PdCl₄]₂-绝对优势组态存在,Pt(Ⅳ)以PtCl₆]₂-为主、PtCl₄]和PtCl₅]-并存的多组态存在,Te(Ⅳ)随pH的变化形成不同酸根离子组态,在强酸性条件下主要形成H₃TeO₃⁺。钯单一体系还原碲捕集贵金属主要形成PdTe₂,铂单一体系还原碲捕集贵金属主要形成PtTe₂和Pt₂Te₃,金单一体系还原碲捕集贵金属产物主要为单质Au和Te,并有少量AuTe_1.7物相。沉金后液中碲捕集铂、钯主要形成碲化物,碲捕集金主要形成单质金及少量碲化物。

Configuration Characteristics of Rare and Precious Metals and Mechanism of Gold,Platinum and Palladium Captured by Tellurium of Degoldized Solution

Copper anode slime(CAS)is a by-product produced in the process of copper electrolytic refining,and it contains multiple valuable-elements such as selenium,tellurium,gold,silver,platinum and palladium.CAS subjected to pyrometallurgical and/or hyrometallurgical process for precious metals extraction,most platinum and palladium are enriched in the degoldized solution,as well as partial rare metals selenium and tellurium,so degoldized solution was an important raw material for recovery platinum group metals.Sulphurous acid was adopted as the efficiency reductant for degoldized solution,it had the advantages of high capture efficiency and low impurity content in concentrate,the mainly components of reduction products were rare metals such as selenium and tellurium.The mechanism of rare metals capture precious metals was considered that freshly formed colloid selenium and tellurium have strongly adsorption capacity for fine particles of precious metals,but it was lack of theoretical support.The possible electrode reactions of rare and precious metals in the process of chlorination leaching gold were analyzed.The valence states of gold,platinum,palladium and tellurium in degoldized solution were analyzed,based on gold reduction potential.According to the thermodynamic relationship between the accumulated stability constants of noble metals complexes and the ligand of chloride ions,the multi-form component diagrams of gold,platinum,palladium and tellurium were calculated and drawn to clarify the existing forms of metal ions in degoldized solution.Sulphurous acid reduction products of gold,platinum and palladium captured by tellurium were characterized by XRD and SEM.The mechanism of gold,platinum and palladium captured by tellurium was analyzed based on geochemical principles and HSAB theory.In the process of gold chloridizing leaching,the solution potential should be controlled to be greater than 1.005 V,and gold dissolves to form trivalent complex,platinum was oxidized to Pt²⁺and Pt⁴⁺,palladium was oxidized to Pd²⁺and Pd⁴⁺,and tellurium could be oxidized to Te⁴⁺and Te6+,respectively.The valence states of gold,platinum,palladium and tellurium in precious solution were Au³⁺,Pt²⁺,Pt⁴⁺,Pd²⁺,Pd⁴⁺,Te⁴⁺,Te6+respectively.In the reduction process of precious solution,it was necessary to control lower potential to precipitate gold,Pd⁴⁺and Te6+were reduced to Pd²⁺,Te⁴⁺,due to the thermodynamic stability area in aqueous solution of Pt²⁺was narrower,Pt²⁺easily oxidized to Pt⁴⁺.The valence states of gold,palladium and tellurium were Au³⁺,Pd²⁺and Te⁴⁺,Pt²⁺and Pt⁴⁺coexisted,and Pt⁴⁺was dominant,in degoldized solution.Au(Ⅲ)could form Au(OH)3 in alkaline condition,Au(OH)₃ was amphoteric compound and mainly display acidic,it could be dissolved in strong alkaline solution to form Au(OH)₄^-,which could be dissolved in acidic solution to formAu(OH)₄-nCln]-(n=1,2,3,4).When lgCl_-]>-4,Au(Ⅲ)formsAuCl₄]-,and coordination numbers of chloride ion was 4.Au(Ⅲ)existed asAuCl₄]-form in degoldized solution.Pt(Ⅱ)and Pt(Ⅳ)mainly formPtCln]2-n(n=1,2,3,4),PtCln]4-n(n=1,2,3,4,5,6)respectively,in the solution contains Cl^-.Pt(Ⅱ)mainly existed as Pt²⁺form at the solution chloride concentration below 10^-7 mol·L^-1,then Pt(Ⅱ)was mainly in the forms ofPtCl]+,PtCl2]andPtCl3]-,at 1×10^-5 to 1×10^-2 mol·L^-1 of chloride concentration,Pt(Ⅱ)mainly exist asPtCl4]2-in strong acidic solution,such as degoldized solution.Pt(Ⅳ)exist as Pt⁴⁺form when Cl-below 10-7 mol·L^-1,with the increase ofCl-],Pt⁴⁺gradually complexed with chloride ions to form corresponding complexes.WhenCl-]was about 1 mol·L^-1,PtCl₄],PtCl₅]^-andPtCl₆]2^-coexisted.Pt(Ⅳ)existed in various forms such asPtCl4],PtCl5]-andPtCl6]2-in degoldized solution.The existence of Pd(Ⅱ)in solution was relative simple,Pd(Ⅱ)was mainly in the form ofPdCl4]2-at acidic solution whichCl-]greater than 0.3 mol·L^-1.Te(Ⅳ)could exist as H₃TeO³⁺,H₂ TeO3,HTeO32-and TeO32-in solution,at strong acidic solution exist as H3TeO3+.Tellurium belonged to the chalcogen,the properties similar to sulfur,which was an electron donor and belongs to soft base ligand,Pt²⁺,Pt⁴⁺and Pd²⁺were electron acceptors and belonged to soft acid ions,based on HSAB theory tellurium was easily to combine with Pt²⁺,Pt⁴⁺and Pd²⁺to form telluride compounds.The reduction product of palladium captured by tellurium was PdTe₂,and the microstructure of which was spherical and ellipsoidal in size about 50 nm.PtTe2 and Pt2Te3 were the main products of platinum captured by tellurium,the microstructure was irregular and the particle size was about 10 nm.The reduction products of gold captured by tellurium were elemental gold,tellurium and AuTeL7,which were spherical or ellipsoidal with uniform particle size and about 50 nm in diameter.The valence states of gold,platinum,palladium and tellurium in degoldized solution were Au3+,Pt²⁺,Pt⁴⁺,Pd²⁺and Te⁴⁺,respectively.The multiform of gold,platinum and palladium were changed with concentration of chloride ion,Au(Ⅲ)mainly existed as AuCl₄^-,Pt(Ⅱ)and Pd(Ⅱ)mainly exist asPtCl₄]2^-andPdCl₄]2^-,and Pt(Ⅳ)mainly coexist asPtCl₄],PtCl₅]-andPtCl₆]₂^-,Te(Ⅳ)forms different acid ion configurations with the change of pH,and H3 TeO3+was the mainly form under strong acidic conditions.PdTe₂ was the main product by reduction of tellurium capture precious metals in a single palladium system,PtTe₂ and Pt₂Te₃ were main products by reduction of tellurium capture precious metals in platinum single system,and the products of tellurium capture precious metals in gold single system were mainly Au,Te and AuTeL7.Tellurium capture platinum and palladium mainly to form telluride,and tellurium capture gold mainly to form elemental gold and a small amount of gold telluride.