Mineral metal cyanide complexes

Abstract In this chapter, the depression mechanism of five kinds of depressants is introduced respectively. The principle of depression by hydroxyl ion and hydrosulphide is explained which regulates the pH to make the given mineral float or not. And so the critical pH for certain minerals is determined. Thereafter, the depression by cyanide and hydrogen peroxide is narrated respectively which are that for cyanide the formation of metal cyanide complex results in depression of minerals while for hydrogen peroxide the decomposition of xanthate salts gives rise to the inhibitation of flotation. Lastly, the depression by the thio-organic such as polyhydroxyl and poly carboxylic xanthate is accounted for in detail including die flotation behavior, effect of pulp potential, adsorption mechanism and structure-property relation. 

To determine total cyanides in solutions containing both simple cyanides and metal cyanide complexes, more drastic conditions are necessary to decompose the complexes, before the HCN is distilled off. Decomposition of complex cyanides occurs on heating with non-volatile mineral acids (H2SO4, H3PO4) in the presence of, e.g., EDTA or tartaric acid [4]. The cyanide complexes of Zn, Cd, Ni, and Fe(III) are decomposed fairly rapidly. On the other hand, Co(III), Fe(II), Cu, Hg, and Pd complexes are decomposed only with difficulty. Decomposition of this latter group requires a long heating. 

Investigations of cyanides and cyano complexes of Cd and Hg have augmented tremendously since about 1990, after detection of inclusion compounds of Cd(CN)2. A thorough review on transition-metal cyanides especially emphasizes the chemistry of inclusion compounds of both the Hofmann type (frameworks dominated by planar Ni(CN)4 building blocks) and the cyanocad-mate type (frameworks with tetrahedral Cd(CN)4 units).87 The structures of these inclusion compounds, but also of cyanides themselves, often topologically resemble the structures of minerals this aspect ( mineralomimetic chemistry ) is dealt with in a simultaneous survey.88 A more generic review of framework structures, with a section on cyanide inclusion compounds, is also to be mentioned.90... 

In the plating industry, rinse waters contain many of the following contaminants, usually in intolerable amounts hexavalent chromium sodium cyanide complex cyanides of the heavy metals, such as cadmium, copper, zinc, and sometimes silver and gold soluble nickel salts strong mineral acids and strong alkalis. Of these, the most toxic are the hexavalent chromium and cyanide ions. 

As a further example of the reduction procedure in groups containing a Coo axis we will consider the symmetry labels for the 6p- and 5d-orbitals of the Au atom in the complex Au(CN)2. This cyanide complex of Au+ is important in gold production because it is used in the recovery of the metal ion from aqueous solution formed using mineral ores. It is another linear molecule belonging to the point group, as illustrated in Figure 5.26. 

Silver is widely distributed throughout the world. It rarely occurs in native form, but is found in ore bodies as silver chloride, or more frequently, as simple and complex sulfides. In former years, simple silver and gold-silver ores were processed by amalgamation or cyanidation processes, The availability of ores amenable to treatment by these means has declined. Most silver is now obtained as a byproduct or coproduct from base metal ores, particularly those of copper, lead, and zinc. Although these ores are different in mineral complexity and grade, processing is similar. 

Depressants (or deactivators) are chemicals that ensure that undesired particles remain hydrophilic and therefore do not get floated. Conversely to the activation of zinc sulfide by copper ions above, zinc ions from zinc sulfate act as a depressant for zinc sulfide. Another example is the use of cyanide to complex with copper and prevent adsorption of collectors in the flotation of base-metal sulfides with xanthates. There are many other depressants but they tend to be quite specific to one of a few types of minerals. In some cases, such as some uses of cyanide as a depressant, the mechanism of depressant action remains unclear. 

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