Mechanism of autoclave-oxidative leaching of activated pentlandite

Abstract

We have shown previously that a prior mechanical treaement of pyrrhotite concentrate in a hlgh-power stressing apparatus, i.e., in an M-3 batch-operated planetary mill, facilitates autoclave-oxldatlve leaching (AOL) of pyrrhotlte. Nickel extraction into solutlon increases thereby 1.8-2.8 times [i]. Pentlandite (Fe, Ni),Se is the most widespread sulfide containing this el~m~nt. It is the principal ore component of the pyrrhotlte concentrate. Therefore, study of its behavior in the autoclave process is of both theoretical and practical interest.The kinetics of oxidation of nonactlvated pentlandlte in the autoclave leaching process was described in [2] and the data on its relative rate were reported in [3]. The dependence of the latter on the sulfide surface exposition was shown in [4].The pentlandlte* isolated by us from the ~re is akin in chemical composition (Table i) to the cubanite ore sample described in [5]. A slight excess of copper in it is perhaps associated with adventitious cubanlte. The mineral was activated mechanically in M-3 in water. The S:L ratio was 1:1.5, the (Fe, Ni)gS8 sample weight was 25 g, and the weight of the remaining milling bodies of 3---, diameter was 500 g. The mechanical treatment time varied from 0.5 to 30 min. The x-ray phase analysis (XPA) of the activated samples and the leaching products was performed on a DEON-2.0 x-ray dlffractometer with a recording rate of 2~The mineral was leached in a l-dm 3 autoclave with mechanical stirring and electric heating (14 g pentlandlte, 700 ml water). Oxygen was passed through the pulp. The experiments lingered for 2 h. Samples were taken from the autoclave for analysis every 5, i0, 15, 30, 45, 60, and 90 mln. The degree of pyrrhotlte decompositions, pH, and the redox potential of the liquid phase were determined in the course of the experiments. The leaching temperatures were 108 and 130~ and the oxygen pressure was 5 arm. A part of the experiments was carried out by bubbling the pulp with oxygen at 90~Results. Mechanical activation remarkably alters the physicochemlcal properties of pentlandite [6,7]. Similar transformations are also observed when a mineral sample taken for AOL experiments is treated in M-3. This is obvious from a comparison of r_he thermal stabillty of the activated and original fractions when heated in air and from the change in the chemical composition due to partial oxidation of the mineral to sulfates (see Table i).The results of nickel extraction on AOL from a nonactlvated pentlandite show that the extent of extraction at the same oxygen pressure depends on the temperature (Fig. i, curves 2 and 3) and reaches 80Z at 130~ Pretreatment of the mineral in M-3 greatly intensifies nickel extraction into solution (Fig. lb) even when bubbling takes place at 90~ and the time in which this element is extracted fully decreases to 30 mln when autoclaved at 130~ On longer (30 min) mechanical activation of (Fe, Ni)gS,, nickel passes in the AOL process almost completely into the liquid phase Just in i0 min. The dependence of this para...

Development of Cryptocrystalline Graphite Desulfurization Methods

“…FeS and FeS2, when they are subject to grinding in moist environment. It has been proved [19,20] that when pyrites are activated in the wat mode, the oxidation process proceeds more intensively than in the air atmosphere. The proof of this fact is the revelation of sulfate ions in the filtrate after mechanical activation of FeS2, magnetite is found in the solid phase.…”

Phase transformations of mechanically activated bornite in autoclave oxidative leaching

“…The sulfuric acid content in the original pulp was 5 g/liter and the solid to liquid ratio was 1:40. Under these conditions the degree of copper extraction into solution, which was taken as the criterion of bornite decomposition, was 50-55% and the relative sequence of the minerals in terms of their leaching rate was troilite, pyrrhotite, pentlandite, bornite, chalcopyrite, cubanite, talnakhite, and pyrite.It was shown earlier [3] that CusFeS ~ oxidation accelerates appreciable in the bacterial leaching process after its preliminary mechanical activation.The purpose of this work was to clarify the effect of bornite treatment in a planetary mill on the mechanism of its autoclave oxidative leaching (AOL).It has been proved in recent years that similar treatment of pyrrhotite, pyrrhotite concentrate, and pentalandite alters their physicochemical proeprties markedly [4,5] and renders their autoclave leaching more effective [6,7]. The x-ray structural and thermal characteristics of bornite after its activation in an M-3 planetary mill (designed by S. I. Golosov) and the kinetics of its oxidation upon heating are also altered markedly [8,9].…”