RU2441084C2 - Method of molybdenum concentrate processing - Google Patents

Abstract

FIELD: metallurgy. ^ SUBSTANCE: concentrate is subjected to two-stage oxidising roasting. Note here that, before first stage, said concentrate is mixed with sulfur-binding additive to perform first roasting stage at 550-650C for 15-30 min. Prior to second roasting stage, molybdenum concentrate is added to calcine produced at first stage in amount of 10-30 wt % from concentrate used in first roasting step. Second roasting is performed at 600-670C for 30-40 min with subsequent leaching of molybdenum and rhenium from calcine obtained in first step. ^ EFFECT: higher yield of molybdenum. ^ 2 tbl, 2 ex

Description

The invention relates to the metallurgy of non-ferrous metals, in particular to methods for the integrated processing of sulfide (molybdenite) concentrates, and can be used to extract molybdenum, rhenium and non-ferrous metals.

Known methods of processing molybdenum concentrates based on:

- a combination of oxidative firing and leaching of molybdenum from the cinder;

- sublimation of molybdenum from cinder and subsequent capture of molybdenum trioxide;

- leaching of molybdenum directly from the concentrate with nitric acid.

The most widely used methods of processing sulfide molybdenum concentrates, including their oxidative roasting, accompanied by the formation of sulfur dioxide, leaching of molybdenum from the cinder and the allocation of marketable molybdenum trioxide (1. Zelikman AN, Meerson G.A. Metallurgy of rare metals (study guide for universities) .M., Metallurgy, 1973, 608 p.).

Sulfur dioxide is disposed of in one way or another. Rhenium contained in concentrates is sublimated in the form of Re ₂ O ₇ ; at sufficiently high amounts, it is recovered during the purification of sulphurous gases.

The most significant operation of this technology is firing. For hydrometallurgical processing of cinder, concentrate is fired in conditions in which sulfur is completely removed and molybdenum forms an easily soluble trioxide. During the oxidation process, the molybdenite particles are coated with the shell of the resulting molybdenum trioxide. Therefore, the rate of the firing reaction, as in all similar processes, is determined by the structure of the oxide shell through which oxygen and sulfur dioxide must diffuse in opposite directions. At temperatures above 500 ° C, the molybdenite mineral is intensively oxidized by atmospheric oxygen with the formation of molybdenum trioxide by an exothermic reaction:

MoS ₂ + 3,5O ₂ → MoO ₃ + 2SO ₂ .

Without access, as well as with a lack of oxygen in the cinder at 600-700 ° C, molybdenum dioxide appears:

MoS ₂ + 6MoO ₃ → 7MoO ₂ + 2SO ₂ .

Since molybdenum dioxide is practically insoluble in ammonia water, it is necessary to carry out firing at a temperature not exceeding 600 ° C in order to exclude sintering of the material and the reaction between MoS ₂ and MoO ₃ . The speed of the process under these conditions is relatively low and when firing on hearth furnaces, the required duration of complete oxidation of sulfur is at least 2-3 hours.

Firing in fluidized bed furnaces proceeds faster, but large dust removal (up to 70%) and material turnover reduce productivity.

A significant drawback of traditional technology is the need to organize the redistribution of sulfur dioxide utilization. The costs of the submitted operation are comparable to the costs of firing.

The capture of rhenium from firing gases and its subsequent extraction from the resulting products is accompanied by significant losses, multi-stage and technologically difficult.

Closest to the proposed technical solution is a method of processing molybdenum concentrate, including oxidative firing at a temperature of 550-600 ° C, which is carried out in two stages: the first stage is carried out with a lack of oxygen to a degree of desulfurization of the cinder 85-95%, the second stage is carried out until complete oxidation sulfur and the formation of metal oxides with an excess of oxygen in 1.5-2.0 times in relation to stoichiometry. At the same time, the volatile oxides of rare metals are distilled off and then captured by absorption (2. RU 2191840, IPC C22B 34/34, publ. 10.27.2002).

The method increases the extraction of rhenium and other rare metals in the gas phase to 93-95%, increases the extraction of rhenium and other rare metals to 2.4-3.3 g / l in absorption solutions, reduces the sulfur content in the cinder to 0.5%; easy to implement; provides environmental friendliness of the process by reducing the concentration of sulfuric acid in solutions.

The disadvantage of the prototype is the insufficiently high extraction of molybdenum in the solution during leaching of the cinder, as well as the need for disposal of exhaust gases.

The present invention is aimed at eliminating this drawback and aims to increase the extraction of molybdenum and simplify the technology based on the exclusion of the operation of the exhaust gas utilization.

To achieve this goal, before the first stage of firing, the molybdenite concentrate is mixed with an additive that binds sulfur, the first stage of firing is carried out at a temperature of 550-650 ° C for 15-30 minutes, before the second stage of firing, molybdenite concentrate is added in the amount obtained after the first stage of calcination in the amount of 10-30 wt.% Of the concentrate used in the first stage of firing, the second stage of firing is carried out at a temperature of 600-670 ° C for 30-40 minutes, followed by leaching of molybdenum and rhenium from the cinder obtained after the second stage of firing ka.

The essence of the invention lies in the fact that at the first stage of firing, carried out in the presence of additives that bind sulfur, for example CaO, Ca (OH) ₂ , the process is carried out at the highest possible speed at the indicated temperatures. In this case, molybdenum and sulfur bind to form calcium molybdate CaMoO ₄ . Rhenium also remains in the cinder in the form of heat-resistant calcium perrenate. The release of sulfur and rhenium in the gas phase does not occur. The presence of heat-resistant components eliminates sintering and aggregation of the cinder.

In the second stage of firing, the amount of added molybdenite concentrate is by weight 10-30% of the initially loaded.

Studies have established that calcium molybdate interacts with molybdenite:

MoS ₂ + 2CaMoO ₄ + 1,5O ₂ = 2CaSO ₄ + MoO ₃

as a result, all molybdenum passes into a soluble form. The thermodynamics of this reaction also determines the high speed and completeness of the flow.

Thus, in this method, it is possible to combine the elimination of the emission of sulfur and rhenium into the atmosphere, the high speed of the process and the completeness of the conversion of molybdenum into a soluble form.

As applied to firing of molybdenite, studies have shown that calcium oxide and hydroxide, calcium carbonate or sodium can be used as sulfur-binding additives.

The firing parameters by stages and the dosage of sulfur-binding additives were determined empirically and can be illustrated by the following data.

Example 1. A portion of a molybdenum concentrate containing 37% molybdenum and 80 g / t rhenium was mixed with CaO lime. Lime consumption was 130% of the stoichiometrically necessary for the binding of sulfur to sulfate. The amount of added concentrate to the cinder in the second stage is 20% by weight of the initial sample. The mixture was fired in a muffle furnace on baking sheets with stirring in various modes in one and two stages.

The cinder was leached under standard conditions: a 10% solution of ammonia when heated to 60 ° C at a ratio of T: W = 1: 4. Ammonia consumption was 140% of stoichiometric. The cake was washed twice. A sample was taken from the combined solution and analyzed for the content of molybdenum and rhenium. Based on the data obtained, the calcination rate and the completeness of molybdenum extraction were calculated. For comparison, one weighed was fired in two stages according to the method of the prototype. The results are shown in table 1.

Table 1. The results of firing and leaching experiments Experience number Firing conditions The total will continue. firing, min Recovery in solution,% Stage 1 2 stage Temperature ° С Min. Temperature ° С Min. Mo Re one 500 fifteen 550 twenty 35 48 51 2 500 40 550 40 80 63 53 3 550 fifteen 600 twenty 35 87 78 four 650 twenty 600 thirty fifty 93 84 5 650 thirty 670 40 70 97 88 6 700 40 700 fifty 90 95 89 Firing according to the prototype method 150 88 19

Example 2. It differs from example 1 (experiment 5) in that in the experiments we varied the amount of concentrate added to the cinder in the second stage of firing.

Table 2. Additive Dosage Results The amount of concentrate added in the second stage,% by weight of the initially loaded Recovery in solution,% Mo Re 5 78 69 10 91 83 twenty 95 85 thirty 97 88 40 96 89

Comparative analysis of well-known technical solutions, including the method selected as a prototype, and the alleged invention allows to conclude that it is the totality of the claimed features ensures the achievement of the perceived technical result. Implementation of the proposed technical solution makes it possible to increase the extraction of molybdenum during cinder leaching by 5-10%, reduce the firing time by 1.5-2 times and simplify the technology by eliminating the operation of utilization of sulfur-containing gases.

Claims (1)

A method of processing molybdenite concentrate, including oxidative roasting of the concentrate in two stages, characterized in that before the first stage of roasting, the molybdenite concentrate is mixed with an additive that binds sulfur, the first stage of roasting is carried out at a temperature of 550-650 ° C for 15-30 minutes, before the second by the firing stage, molybdenite concentrate is added to the cinder obtained after the first stage in the amount of 10-30 wt.% of the concentrate used in the first firing stage, the second firing stage is carried out at a temperature of 600-670 ° C for 30-40 m with subsequent leaching of molybdenum and rhenium from the cinder obtained after the second stage of firing.