Cyanide depression

The use of a non-cyanide depressant system resulted in a substantial improvement in gold recovery in the copper concentrate. 

The depression of pyrite by cyanide has been considered from the electrochemical viewpoint, the formation of ferric ferrocyanide in the surface of pyrite which was perhaps responsible for cyanide depression was proposed by Ball and Richard (1976) to occur by the following electrochemical reaction. 

Activators enhance the adsorption of collectors, eg, Ca " in the fatty acid flotation of siUcates at high pH or Cu " in the flotation of sphalerite, ZnS, by sulfohydryl collectors. Depressants, on the other hand, have the opposite effect they hinder the flotation of certain minerals, thus improving selectivity. For example, high pH as well as high sulfide ion concentrations can hinder the flotation of sulfide minerals such as galena (PbS) in the presence of xanthates (ROCSS ). Hence, for a given fixed collector concentration there is a fixed critical pH that defines the transition between flotation and no flotation. This is the basis of the Barsky relationship which can be expressed as [X ]j[OH ] = constant, where [A ] is the xanthate ion concentration in the pulp and [Oi/ ] is the hydroxyl ion concentration indicated by the pH. Similar relationships can be written for sulfide ion, cyanide, or thiocyanate, which act as typical depressants in sulfide flotation systems. 

Depressants are reagents that selectively prevent the reaction between a coUector and a mineral, thus preventing its flotation. For example, sodium cyanide [143-33-9] depresses sphalerite [12169-28-7] (zinc sulfide) and pyrite [1309-36-0] (iron sulfide) but not galena. It thus enhances selective flotation of the galena. 

Zinc ores are generally floated at the mine (18). In the case of simple zinc sulfide ores, flotation is carried out by treatment with copper sulfate to activate the sphalerite causing it to be wet by the organic collector (eg, xanthate). The now-hydrophobic zinc ore particles attach themselves to the rising bubbles. Oxidized ore particles present must be sulftdized with sodium sulfide to be floated (19). Flotation produces concentrates which are ca 50—60% zinc. In mixed ore, the lead and copper are usually floated after depressing the sphalerite with cyanide or zinc sulfate. The sphalerite is then activated and floated. 

The pH of the pulp to the flotation cells is carefliUy controlled by the addition of lime, which optimizes the action of all reagents and is used to depress pyrite. A frother, such as pine oil or a long-chain alcohol, is added to produce the froth, an important part of the flotation process. The ore minerals, coated with an oily collected layer, are hydrophobic and collect on the air bubbles the desired minerals float while the gangue sinks. Typical collectors are xanthates, dithiophosphates, or xanthate derivatives, whereas typical depressants are calcium or sodium cyanide [143-33-9] NaCN, andlime. 

A thiazole derivative that incorporates a fragment of the amphetamine molecule shows some CNS stimulant activity more specifically, the compound antagonizes the depression caused by overdoses of barbiturates and narcotics. Reaction of benzalde-hyde with sodium cyanide and benzenesulfonyl chloride gives the toluenesulfony1 ester of the cyanohydrin (141). Reaction of this with thiourea leads directly to aminophenazole (143) It is probable the reaction proceeds by displacement of the tosylate by the thiourea sulfur to give 142 addition of the amino group to the nitrile followed by tautomerization affords the observed product. ... 

A. Hausberger As we mentioned earlier, the light hydrocarbons do not seem to affect catalyst activity, and they do reform into methane. However, you can increase the hydrocarbon content to levels where they do depress the methanation activity. If the hydrocarbons are high enough in unsaturation, they will form carbon when they get to a certain level. As far as hydrogen cyanide and ammonia are concerned, we don t expect them to affect the nickel methanation catalyst. 

The development of more benign alternatives to cyanide for gold-leaching (see Section 9.17.3.1) such as thiourea, thiocyanate, or thiosulfate, which form stable complexes in water has prompted research to identify suitable solvent extractants from these media. Cyanex 301, 302, 272, Ionquest 801, LIX 26, MEHPA, DEHPA, Alamine 300 (Table 5) have been evaluated as extractants for gold or silver from acidic thiourea solutions.347 Whilst the efficacy of Cyanex 301 and 302 was unaffected by the presence of thiourea in the aqueous feed, the loading of the other extractants is severely depressed. Formation of solvated complexes of gold and of an inner-sphere complex of silver has been proposed.347... 

Cyanide is used to depress pyrite, since some of the ore types contain an appreciable amount of pyrite. The results obtained in the plant are presented in Table 20.8. 

Asphyxia has been observed in rats exposed to 250 ppm cyanogen (125 ppm cyanide) for 7.5-120 minutes (McNemey and Schrenk 1960), asphyxia and pulmonary edema were observed in dogs exposed to concentrations ranging from 149 to 633 ppm hydrogen cyanide (143-608 ppm cyanide) for 2-10 minutes (Haymaker et al. 1952), while severe dyspnea was observed in monkeys exposed to 100 ppm hydrogen cyanide (96 ppm cyanide) for 30 minutes (Purser et al. 1984). Exposure to 63 ppm hydrogen cyanide (60 ppm cyanide) for 30 minutes resulted in a 50% decrease in respiratory rate of mice due to depression of the respiratory center (Matijak-Schaper and Alarie 1982). 

Sun et al. (1995) reported that the nitric oxide generator, isosorbide dinitrate, is an effective cyanide antidote in mice. They showed that the mechanism does not involve methemoglobin formation and suggested that nitric oxide might antagonize the respiratory depressant effects of cyanide. Other more efficient nitric oxide generators may be very useful cyanide antidotes. 

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. 

Keywords depressant hydroxyl ion hydrosulphide ion cyanide hydrogen peroxide thio-organic... 

Modifiers in the flotation of sulphide minerals mainly include depressants and activators. A depressant is defined as a reagent which inhibits the adsorption of a collector on a given mineral or adsorbed on the mineral to make the siuface hydrophilic, and includes inorganic depressants such as lime, sodium cyanide, sulphin dioxide, zinc sulphate, sodium sulphide etc., and organic depressants such as sulfhydryl acetic acid, polyacrylamide polymers containing various functional groups etc. In this chapter, roles of depressants in the flotation sulphide minerals will be discussed and some new organic depressants will be introduced. 

Janetski et al. (1977) also studied the behavior of a pyrite electrode in a solution of cyanide concentration in the absence and presence of xanthate using voltammetric technique. They reported that on increasing the concentration of cyanide at constant pH and xanthate concentration, the oxidation wave of xanthate is shifted to more anodic potential indicating that the presence of cyanide, which may react with the mineral surface to form an insoluble iron cyanide complex will result in the inhibition of the electrochemical oxidation of xanthate and the depression of pyrite. 

Carbon monoxide binds to cytochrome a/Oj but less tightly than cyanide. It also binds to hemoglobin, displacing oxygen. Symptoms include headache, nausea, tachycardia, and tachypnea. Lips and cheeks turn a cherry-red color. Respiratory depression and coma result in death if not treated by giving oxygen. Sources of carbon monoxide include ... 

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