Natural and caustic magnesite should be beneficiated to a content of at least 98% MgO by chemical methods, including the hydrochloric acid method [1, 2].The East Institute of Refractories is planning a prototype unit with a capacity of 400 tons per annum using the acid method and natural magnesite with hydrolysis of magnesium chloride. This article gives the results of a study aimed at tightening up the parameters for beneficiating these two forms of magnesite with the acid method.The starting materials consisted of natural magnesites II and IV in the form of fractions --3 and --8 ram, and also ~milled (ballmill) material down to fractions --0.5 ram, including 40-50% fractions --0.063 ram, dolomite fractions --8 mm (the main mechanical impurity in the magnesite raw material) and magnesite caustic dust from the cyclones and electric filters. The dust from the cyclones in the form of fractions --0.5 mm contained 67% particles --0.063 mm and its specific surface was 2.3 m2/g; the dust with a specific surface of 4.7 m2/g from the electric filters contained 98% fractions --0.063 mm.One of the decisive processes in the acid benefieiation method for magnesite is the solution in the acid, and so we studied the kinetics of solution for rocks, minerals, and materials as a function of the grain sizes, the concentration, and temperature of acid. The rate of solution of magnesites was assessed from the weight and chemical composition of the insoluble part of the material being studied in a certain time interval (Table 1)o The magnesite was dissolved in hydrochloric acid of 12.5 and 20% concentration with 10 and 20% excess against the stoichiometric, and in this case the ratio of liquid and solid substance was for natural magnesite 8 : 1, and for caustic 14 : 1. Since the solution of natural magnesite occurs only during heating (hot-solution method) the acid temperature and solution temperatures were maintained at 80-85~The caustic magnesite was dissolved at 80-8 5~ and also at room temperature (cold-solution method). r, min r, rain The natural magnesite and the residual magnesium carbonate in the caustic dust were decomposed by the acid according to:MgCOa + 2HC1 8~176176 Y~gCI2 + H20 + CO21.The difference in the degrees of solution of magnesite in HC1 of different concentrations is zero; in 2 h in both cases about 85% of magnesite passes into solution. Natural magnesite in fractions --8 and --3 mm is dissolved at about the same rate. The kinetic curves for the solution ~ of natural magnesite and extraction e of oxides into solution are shown in Figs. 1 and 2. Figure 1 shows curves with three sections for the change in the solution rate of magnesite, fast (I5, slow (II), and weak (III) solubility.During the first 15 min in section I the rate of solution is 2.7, and in section IT 0.5%/min; later, the rate diminishes to 0.08%/rain (Bee Fig. lb).This change in the rate of solution of magnesite and other carbonate impurities in the raw material (dolomite, calcite, breunerite 5 is determined by the rate of the diffusion processes...
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