Depression galena

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. 

Figure 4.11 shows three cycles of the voltammograms of the galena electrode at pH= 12.8 with DDTC concentration 4x10 mol/L. Because of the high DDTC concentration, the oxidation of galena itself is depressed. The anodic current peak of PbD2 arises evidently at 0-0.2V. However, the anodic currents decrease in... 

Then, galena will be depressed. The critical pH determined by decomposition reaction is defined by... 

Therefore, the critical pH of hydroxyl depression of pyrite and galena could be calculated using Eqs. (5-4) to (5-8) or Eqs. (5-9) to (5-11). The results are given in Fig. 5.1 for the diethyl dithiophosphate system and in Fig. 5.2 for the ethyl xanthate system. Also shown in the same figures are the so-called contact curves (solid lines) from Sutherland and Wark (1955). The dashed lines are the calculated... 

Lime is a special kind of hydroxyl depressant and usually used for depressing pyrite in plant, which has sponger depression on pyrite than other alkaline depressants at the same pH condition (Fuerstenau, et al., 1968 Hu et al, 1995). Figure 5.3 shows that at pH= 12 modified by CaO and NaOH, galena is fairly floatable and pyrite is depressed. CaO is a stronger depressant than NaOH. 

Therefore, the critical pH of hydrosulphide ion depression of pyrite and galena could be calculated using Eqs. (5-15) and (5-16). The results are plotted in Fig. 5.13. The same figure is the results of contact curves reported by Wark and Cox (1933). It can be seen from Fig. 5.13 that the critical pH condition defined by electrochemical equilibrimns of Eqs. (5-15) and (5-16) is correlated reasonably well with the contact curves. The calculated concentration of sodium sulphide required for preventing the interaction between xanthate and galena or pyrite at... 

Therefore, at certain pH and H2O2 concentration, the complete decomposition of lead xanthate preadsorbed on galena renders galena surface hydrophilic and depression of galena, whereas the dixanthogen prefixed on chalcopyrite remains stable which confers chalcopyrite surface hydrophobic and floatable, which was proved by voltammogram method (Wang, 1992). 

The conditional stability constant of various metallic ions can be obtained as a function of pH, using this equation along with the resultant log /3 -pH diagram shown Fig. 4.47. The diagram shows that Cu " ", Fe +, Zn + ions can form stable complexes so that cyanide is a depressant for sulfides of copper, zinc and ferrous. However, lead ion cannot form stable cyanide complexes and thus does not depress the flotation of galena. 

Fig. 4.51. 3-D diagram of depressant-xanthate-pH systems and selective flotation of galena and sphalerite (Wang, 1986).

At [EX ] = 1.56 X 10 " mol/1, the calculated pH value for depression of pyrite at different concentrations of HS is shown as a dashed line in Fig. 4.57, which is in agreement with the experimental data of Sutherland (solid line). At pH > pH, the oxidation of HS ions into SO or S203 will take place before X ions are oxidized to X2 or begin to react with galena, and the mineral will not then be rendered hydrophobic. 

These are used to prevent flotation of one material while floating another. Lime and NaCN are examples. Both of these depress pyrite. Dichromate is a depressant for galena. HF is used to depress quartz in the flotation of feldspar with amine collectors. Sodium silicate is also a quartz depressant. Quebracho depresses calcite and dolomite in the flotation of fluorite with fatty acids. 

Gagarinite structure, 846 Galactose oxidase, 700 copper, 655 Galena brines, 853 depression, 783 dissolution, 787 humic acids, 861 Gallium isotopes... 

The galena would be floated first under conditions of alkaline pH (pH 8-10) using a low concentration of an alkyl xanthate as the collector, sodium sulfite to depress the zinc minerals and a short-chain alcohol as a frother. After galena flotation, the pH would be raised to 11-12 (to depress gangue iron sulfides) copper sulfate is added to activate sphalerite and marmatite additional alkyl xanthate is added to float these two minerals. The final lead concentrate should be more than half lead with minimal zinc content the final zinc concentrate should be more than half zinc with minimal lead content. 

Sodium cyanide is also used as a depressant in the mining industry. A depressant is a reagent that selectively prevents the reaction between a collector and a mineral. In other words, a depressant prevents the mineral from flotation. The use of sodium cyanide, in this case, is to selectively depress sphalerite (zinc sulfide) and pyrite (iron sulfide) but not galena. Sodium cyanide therefore enhances flotation of galena (Kirk-Othmer, 1995b). 

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