Solubility metal-xanthate

When exposed to ait, the sodium salts tend to take up moisture and form dihydrates. The alkah metal xanthates are soluble ia water, alcohols, the lower ketones, pyridine, and acetonitrile. They are not particularly soluble ia nonpolar solvents, eg, ether or ligroin. The solubiUties of a number of these salts are Hsted ia Table 4. Potassium isopropyl xanthate is soluble ia acetone to ca 6 wt %, whereas the corresponding methyl, ethyl, / -propyl, n-huty isobutyl, isoamyl, and benzyl [2720-79-8] xanthates are soluble to more than 10 wt % (12). The solubiUties of the commercially available xanthates ia water are plotted versus temperature ia Figure 1 (14). 

Table 4. Solubilities of Some Alkali Metal Xanthates...

In the initial formation of the cupric xanthates, soluble xanthate complexes form prior to the precipitation of the cuprous xanthate with the concurrent formation of the dixanthogen (51). The dixanthogen can be separated by virtue of its solubiUty in ether. Older samples of alkah metal xanthates contain some dixanthogen, which is thought to form by the following reaction (33) ... 

Many of the heavy metal xanthates have been piepaied from aqueous solutions of the alkah metal xanthates and the water-soluble compound of the heavy metal desired. 

In the 2nd period ranging from the 1930s to the 1950s, basic research on flotation was conducted widely in order to understand the principles of the flotation process. Taggart and co-workers (1930, 1945) proposed a chemical reaction hypothesis, based on which the flotation of sulphide minerals was explained by the solubility product of the metal-collector salts involved. It was plausible at that time that the floatability of copper, lead, and zinc sulphide minerals using xanthate as a collector decreased in the order of increase of the solubility product of their metal xanthate (Karkovsky, 1957). Sutherland and Wark (1955) paid attention to the fact that this model was not always consistent with the established values of the solubility products of the species involved. They believed that the interaction of thio-collectors with sulphides should be considered as adsorption and proposed a mechanism of competitive adsorption between xanthate and hydroxide ions, which explained the Barsky empirical relationship between the upper pH limit of flotation and collector concentration. Gaudin (1957) concurred with Wark s explanation of this phenomenon. Du Rietz... 

TABLE 1. SOLUBILITIES OF SOME ALKALI-METAL XANTHATES... 

A separate group of metal starchates comprises metal salts of starches carrying carboxyl, xanthate, sulfate, phosphate, and similar groups. Oxidized, carboxyalkylated, sulfated, xanthated, and phosphorylated starches readily form corresponding salts by methatetical reactions between the sodium salts of the aforementioned derivatives and other water-soluble, metal salts. There are several patents on the formation of these salts for ion exchangers and the removal of... 

Lipid-soluble metal complexes such as copper xanthates (from mineral flotation plants), copper 8-hydroxyquinolinate (agricultural fungicide) or alkyl-mercury compounds are particularly toxic forms of heavy metals because they diffuse rapidly through a biomembrane and carry both metal and ligand into the cell. ... 

The heavy metal salts, ia contrast to the alkah metal salts, have lower melting points and are more soluble ia organic solvents, eg, methylene chloride, chloroform, tetrahydrofiiran, and benzene. They are slightly soluble ia water, alcohol, ahphatic hydrocarbons, and ethyl ether (18). Their thermal decompositions have been extensively studied by dta and tga (thermal gravimetric analysis) methods. They decompose to the metal sulfides and gaseous products, which are primarily carbonyl sulfide and carbon disulfide ia varying ratios. In some cases, the dialkyl xanthate forms. Solvent extraction studies of a large number of elements as their xanthate salts have been reported (19). 

This technology involves the addition of chemical reagents to cause insoluble compounds to form. A common method nsed to precipitate metal ions is pH adjustment. The desired pH is one in which the metals exhibit low solubilities in water and therefore precipitate. Common reagents nsed for pH adjnstment include aUcahs such as lime, caustic soda, or magnesium hydroxide slurries to precipitate metal hydroxides. Sulfides such as sodium sulfide or ferrous sulfide slurries are often nsed to precipitate metal snlfides. Other reagents, such as xanthates, can also be nsed to precipitate metal ions. 

Quite frequently the natural surface of a mineral requires preliminary chemical treatment before it will form the surface film required for collection One of the commonest instances of this is with sphalerite (zinc sulphide), which does not float properly when treated with xanthates. If, however, it is given a preliminary treatment with dilute copper sulphate solution, a very small amount of copper sulphide is deposited on the surface and the ore becomes floatable, the surface being now capable of reaction with xanthates. Such treatment is usually termed activation in general, an activating solution for a sulphide mineral should contain a metallic ion whose sulphide is less soluble than that contained in the mineral for zinc sulphides, silver, copper, mercury, cadmium, and lead salts are all effective activators. 

Metal-Organics. Many organic materials also form low-solubility species with certain metals. Among these are humic acids. The most widely publicized insoluble substrate for heavy-metal immobilization has been insoluble starch xanthate (ISX). In contact with metal ions, the metal links to the sulfur group much as it would with the S-2 in inorganic sulfides ... 

WI Starch Xanthate. Research by Wing and others (22, 27-29) has shown that water-soluble (WS) starch xanthates, in combination with cationic polymers to form polyelectrolyte complexes, can effectively remove heavy metals from waste water. To eliminate the expensive cationic polymer and give a more economical method of heavy metal removal, further research by Wing and others (12,30-33) showed that xanthation of a highly crosslinked starch yields a water-insoluble (WI) product that is effective in removing heavy metals from waste water without the need for a cationic polymer. In more recent work, Tare and Chaudhari (34) evaluated the effectiveness of the starch xanthate (WS and WI) process for removal of hexavalent chromium from synthetic waste waters. 

A significant development in this regard was the correlation of the solubility products of a series of heavy metal-ethyl xanthate salts with the floatability of corresponding sulfide minerals by (Kakovsky, 1980). He found the decrease in the order of the solubility product of sulfide minerals to be in line with the increase in the order of their floatability. From exchange reactions of lead-diethyl xanthate, the well-known Barsky equation can be derived ... 

Solubility products of collector-metallic ion compounds (see Appendix C) suggest that the sulfide mineral collectors such as xanthates, mercaptans and thiophosphates containing sulfur bonding atom in the minerophilic group can form compounds of low solubility products with ions of elements with affinity for copper(II). They can not form insoluble... 

Collectors for nonsulfide minerals containing O atom, such as fatty acids and sulfonates, react with various metallic ions by ionic bond, and they have high solubility in water. The solubility becomes low only when the hydrocarbon chains in the molecules are long. In contrast, collectors for sulfide minerals, such as xanthates possessing only a short chain, the S bonding atom reacts with metallic ions to form covalent bonds with lower polarity. 

Suliide collectors such as xanthate can react with various metal ions to form various stable complexes and precipitates. Therefore, potentiometric and amperometric titration can be used to test the concentration of sulffde collectors. C. du. Rietz studied the adsorption of xanthate, aeroffoat and fatty acid by means of potentiometric titration. Meantime, hydrolysis and oxidation of xanthate, as well as solubility products of metal compounds of xanthate and fatty acid were determined [2, 3]. In the course of test, the concentration of xanthate was titrated using AgN03 solution. Titration endpoint was calculated according to the electric potentials of silver electrode and calomel electrode. 

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