Study On The Mechanism Of The Formation And Action Of Arsenato Antimonic Acid In Copper Electrorefining

Commercial operation results showed that, by enhancing the self-purification capability of copper electrolyte, the volume of purified electrolyte per ton cathode was markedly decreased, the cost of copper electrorefining was lowered, and the degree of versatility for the feed of copper smelting process in operation was heightened. So the competitive capacity of the product was strengthened in market. Experiments found that As(V) and Sb(V) can form a series of arsenato antimonic acids. Arsenato antimonic acid (AAAc) can further react with As(III), Sb(III) and Bi(III) to form arsenato antimonates that is indissoluble even in strongly acidic solution. The capability of the electrolyte self-purification depends on the amount of arsenato antimonates formed in it during copper electrorefining.The compositions, structures and main physical chemistry properties of AAAc and arsenato antimonates were studied using infrared spectroscopy, Raman spectroscopy, X-ray diffractometer, thermogravi-metric analyzer etc in this paper. The formation mechanism of AAAc and arsenato antimonates in aqueous solution and the technical enhancement of the self-purification capability of copper electrolyte ware discussed.AAAc fall into two categories of chain and network structure AAAc. Arsenic atom, which is in the form of H2AsO3-O-, combines with antimony atom through As-O-Sb bond and is at the terminal part of AAAc molecules in contrast to antimony atom. So H2AsO3-O- can be easily removed from AAAc molecules in strongly acidic solution. Antimony atoms interconnect by [SbO6] octahedron vertex sharing.AAAc(l:l) with As/Sb atom ratio of 1:1 is the simplest. It has a formula of H2[AsO(OH)2O-Sb(OH)4-O-Sb(OH)4-O-AsO(OH)2]. AAAc(l:l) is a hexabasic acid with the dissociation constants of k1=3.62 10-2, k2=3.05xlO'3, k3=6.43xlO-6,k4=9.78xlO-8,k5=1.32xlO-",k6=3.87xlO-12.Chain AAAc has a formula of H.Y[(H2AsO3)vSbvO(.T+v.1)(OH)[,(6.1)+2.x.v]], where y/x is the As/Sb atom ratio with x > 2, y 2o Network AAAc has a formula of H4As2O72/7SbO3H, where l/n is the As/Sb mole ratio0 When n>2, it becomes internal-crystalline nano-molecules (ICNM).The outside of the ICNM is the shell of H2AsO3-O-, the inside is the nano-crystal of the three-dimensional network of vertex-sharing [SbO6] octahedra that form a cubic NaCl-type cell with a lattice parameter of 10.33A, space group Fm3m, 27 HSbO3 clusters per unit cell. The distance of Sb-6-Sb with an angle 116.7 is 3.44A in the unit cell.The elementary reaction of AAAc formation is arsenic acid combines with antimonic acid to form the intermediate of H[H2AsO3-O-Sb(OH)5J. When the intermediate condenses, AAAc are obtained. When it combines with As(III), Sb(III) and Bi(III), covalent arsenato antimonates are formed. The arsenato antimonates are indissolvable even in strongly acidic solution.In the arsenato antimonates, Sb(V) atoms can not only interconnect, but also combine with As(III), As(V), Sb(III) and Bi(III) atoms. As a result, its composition and structure are uncertain, and the arsenato antimonates obtained under normal conditions are amorphous.The specific infrared spectrum of arsenato antimonates was obtained. The bands of v (As-OH) and v (As-OX (X = As, Sb, Bi)) are at 1032 and 817cm-1 respectively, while that of v (Sb-OH) and v (Sb-OY (Y = As, Sb, Bi) are at 619 and 503 cm'1 respectively.It was found that there are two control steps in the formation of arsenato antimonates in copper electrolyte. They are the conversion of Sb(III) to Sb(V) and the combination of H[H2AsO3-O-Sb(OH)5] with As(III), Sb(III) and Bi(III). By increasing the relative content of Sb in anode copper properly and adjusting the concentration of As and the ratio of As(III)/As(V) appropriately, the formation of arsenato antimonates can be speed-upped remarkably and the volume of electrolyte to be purified be decreased greatly.