WO2000046412A1

WO2000046412A1 - Integration processes of the treatments of concentrates or zinc silicates ore and roasted concentrates of zinc sulphides

Info

Publication number: WO2000046412A1
Application number: PCT/BR1999/000103
Authority: WO
Inventors: Adelson D. Souza; Marcelo G. Mendes
Original assignee: Companhia Mineira De Metais
Priority date: 1999-02-05
Filing date: 1999-12-13
Publication date: 2000-08-10
Also published as: BRPI9904195A2; AU1645600A

Abstract

The invention refers to the several forms of integration and gathering of the processes of treatment of ores and zinc silicate concentrates with the calcine from the roaster of sulphides in the zinc industry. These processes comprise using raw concentrates or ores of zinc silicates, from several mineral sources, which are leached together with the calcine from the roaster of zinc sulphides, using raw zinc silicate ores or concentrates, from several mineral sources, interlinking with the treatment of the calcine from the roaster of zinc sulphides, using raw concentrates of ores of zinc silicates, from several mineral sources, interlinking with the treatment, of the calcine from the roaster of zinc sulphides after the silicates leaching, using calcined silicate concentrates or silicates ores, with selective precipitation of zinc, in the magnesium treatment and integration with the calcine from the roaster of zinc's sulphide concentrate.

Description

"INTEGRATION PROCESSES OF THE TREATMENTS OF CONCENTRATES OR ZINC SILICATES ORE AND ROASTED CONCENTRATES OF ZINC SULPHIDES" .

The well-known hydrometallurgic processes of obtainment of zinc in solution consist in the treatment of Sulphide Roaster calcine by neutral leaching through several leachings stages of the ferrites and consequent removal of iron, either by precipitation as jarosite, paragoethite, goethite, haematite or iron slag. The patents GB 2 114 966 A 'Recovery of zinc from sulphidic material", US 5,120,353 'Hidrometallurgic method for processing raw materials containing zinc sulphide", US 5,585,079 'Method for leaching material containing zinc oxide and zinc silicate" and the Brazilian Patent PI 9407223-0 A 'Processes for extraction of Zinc from Concentrates of Zinc Sulphide, and for the leaching of zinc ferrite, jointly with a sulphided material containing zinc sulphide", refer to these processes.

This invention' s purpose is to provide several processes of integration and unification in the treatment of zinc silicate ores and concentrates with the calcine obtained from the sulphides roasting defined by joint or interconnected leaching of these several sources of zinc, their filtrations and joint purification of the solutions of the obtained zinc sulphate. The results are options of simplified processes with elevated performances of recovery of zinc, mainly from the silicate concentrates and ores (increase from 88 % to 97 % in zinc solution, in the treatment of the silicates) .

The use of only one acid leaching for the zinc ferrites has also been achieved through the integrated process with the silicate ores and concentrates, allowing for the obtainment of up to 99.3 % of a zinc solution in relation to this Zinc source.

Integration Process I - shown in the blocks flowchart of Fig. 1.

Fig. 1 shows the option of integration of the treatment processes of sulphide concentrate and silicate (or ore) zinc concentrate, where the integration or linking of the processes occurs in the Neutral Leaching stage. After the magnesium treatment of the concentrate or silicate ore, to extract the magnesium present in the concentrate and in the spent solution from the electrolysis, the silicate cake is pre-leached. In the pre-leaching stage, the carbonates present in the concentrate are dissolved and the acid pulp is driven to the Neutral Leaching of the calcine (arising from the Roasting of the sulphide concentrate) , where it is integrated into the joint zinc extraction process of the two sources of Zinc. The operational conditions, for each stage of this process are described hereinbelow:

Repulping Stage - This stage consists of the repulping of the zinc silicate concentrate with washing waters of the leaching residues, residual waters of the plant or simply industrial water. The operation parameter in this phase of the process is the concentration of the solids, to be kept from 45 % to 60 %. The repulping tank is to be coated with an anti-acid material, to resist the chemical effect, when liquids of high degree of acidity are used.

Stage of Magnesium Treatment - Its purpose is to eliminate part of the magnesium contained in the source of silicates zinc and in the spent solution from the electrolysis. It is suited to control the balance of the plant waters.

The spent solution arising from the stage of the zinc electrolysis is added to the ore pulp/zinc silicated concentrate, so as to maintain the pH ranging from 4.0 to 4.5. Direct or indirect steam is injected in the tanks to maintain a temperature ranging from 75 to 85 °C. Upon such conditions, part of the magnesium and of the zinc contained in the silicate ore is added to the solution. Next, in a series of cascade tanks, it is executed the selective precipitation of the zinc in relation to the magnesium, by adjusting the pH parameters, temperature and residence time. When the zinc concentrations are lesser than 10.0 g/1, it is performed the separation solid/liquid, where the liquid is sent to the stage of recuperation of zinc and the solid part to the ore's or silicates concentrate's pre-leaching stage. The water balance in the plant is done by introduction of a greater or lesser amount of solution spent in this stage. When the balance of water in the plant is unfavorable (increase of the general volume) it is increased the amount of spent solution introduced in this stage and vice-versa, and the favorable balance of water decreases the quantity of spent solution.

Pre-leaching stage of ore/silicate concentrate - This stage consists of the pre-leaching of the pulp with objective to promote the dissociation of the carbonates contained in the silicate ore/concentrate, according to reaction:

MeCθ3+H2Sθ4 MeSθ4+Cθ2+H2θ, where Me = Ca, Mg, Zn, etc.

The pH, in this stage, is kept within the range from 3.0 to 3.5, through the addition of spent solution arising from the zinc electrolysis. The residence time ranges from 3 to 6 hours and varies according to the physical & chemical characteristics of the silicate that is being treated. This stage can be leaded for cold or hot temperatures.

Stage of neutral leaching - It is in this stage that the integration of the process occurs. The two ores (the silicated ore and the zinc sulphide already calcined) are leached together. The leaching is to be performed so as to be obtained the zinc's maximum extraction and the silica coagulation, so that the obtained pulp may be decanted, filtered or centrifuged. Of the several studied parameters it was verified that the most important to obtain a maximum extraction of zinc and coagulation of the silica were: - pH - 3.2 to 3.8.

- Temperature - 70 to 75°C.

- Residence Time: from 4 to 5 hours.

The zinc extraction efficiency in this stage is 80 %. The concentration of soluble silica ifi tήe -i.iuuJ fc.A tests was around 60 to 80 mg/1 in the zinc sulphate solution, which is sent for purification. This concentration of silica didn't harm or decrease the efficiency of the processes of solid/liquid separation of the pulp. Yet in this stage it is made the purification of the elements deemed dangerous to the stage of the electrolysis of the zinc. This purification is made through the precipitation of the iron contained in the solution, in the form of ferric hydroxide. Chemical elements as As, Ge, Sb, Se and Te are purified in this stage. The iron in the first tank has to be kept ranging from 0.5 to 3.0 g/1 and this variation is in accordance with the concentration of these elements deemed dangerous in the ores/concentrates which are being processed. The adjustment of the concentration of iron in the first tank is made by using the liquid from the acid leaching stage. Anode mud containing manganese dioxide is also added in this tank for the oxidation of the Fe++ to Fe+++ .

The pulp obtained in the last tank of Neutral Leaching is thickened, so that an overflow be obtained, such overflow constituted of a zinc sulphate with traces of cadmium, copper, cobalt, nickel, arsenic, germanium, antimony, which goes to the stages of Purification, Electrolysis and Casting. These last phases of the process are not the subject of the Patent. The underflow goes to the Acid Leaching unit, for leaching of the zinc ferrites from the Roaster's calcine, whose later phases are not the subjects of this Patent, as well.

Integration Process II - shown in the blocks flowchart of Fig. 2.

Fig. 2 exhibits another option of connection of the processes of treatment of the zinc sources. In this case, the interlinking occurs in the stages of Acid Leaching of the calcine and/or precipitation of iron, instead of the stage of Neutral Leaching of the previous option. The amount of concentrate or silicaCed ore m each stage may range from zero to one hundred percent. The option to use the integration process I or II depends on:

• whether the plant is already in operation: the availability of equipments in each stage; complexity of lay-out change; physical space for the adaptation; cost/benefit.

• If a new plant: it depends more on the cost/benefit.

Integration Process III - shown in the blocks flowchart of Fig. 3.

Fig. 3 presents the integrated process for the obtainment of zinc, where the silicate concentrate or ore is fully leached and the obtained pulp is sent to the Neutral Leaching of the Calcine of sulphide zinc concentrate.

In this process it is introduced a step denominated silicate leaching followed by a solid/liquid separation. The silicate acid leaching is made with a solution denominated leaching solution, which is a mixture of Concentrated Sulfuric Acid with spent solution from the electrolysis. The concentration of acid in the leaching solution may range from 150 to 250 g/1 and such variation is due to the balance of sulphate in the process. The residence time ranges from 5 to 8 hours and basically depends on the efficiency of agitation in the tanks, granulometry of the ore/concentrate, temperature and the grade of the minerals contained in the source of silicate zinc. The purpose of this stage is to extract the maximum possible of the zinc contained in the silicate source and the parameter to evaluate the efficiency of this stage is the content of zinc soluble in acid (zinc content not leached) discarded in the subsequent stage, which is the separation solid/liquid. The value deemed optimal is ZnH+ < 0.5 %. The process of integration of the two plants is made through the liquid obtained in the stage of separation solid/liquid, which is sent to the neutral leaching. The conditions of the neutral leaching operations are the same ones already described in the item 'Integration Process I". The obtained solid residue is sent to the filtration where the residue washing is accomplished to recover the soluble zinc.

The washing is performed in two stages, re-pulping and displacement and the soluble zinc content contained in the discarded residue is lesser than 0.5 % . Integration Process IV - shown in the blocks flowchart of Fig. 4.

Fig. 4 shows the integration process which has also been industrially tested and contemplates the calcination of the silicate concentrate, aiming at the decomposition of the organic substances and the carbonates contained in the concentrate. The calcination may be acomplished, by using horizontal or vertical batch or continuous kiln, by using fuel oil of any type, gasogene, natural gas, coal fines, etc.

The use of the previously calcinated silicate concentrate eliminates the silicate's pre-leaching step, whose purpose was precisely to promote the decomposition of the carbonates through the chemical process .

The integration of the process can be made:

- By directly adding the silicate calcinate in the stage of neutral leaching.

- By adding the silicate calcinate in the acid leaching stage.

- By adding the silicate calcine in the Precipitation of Iron/Paragoetite phase. - By simultaneously adding the silicate calcine in the two or three phases.

- For all the options above, the silicate calcine may or may not be submitted to the magnesium treatment, jointly with the secondary filtrate from the residue washing or other plant's washing waters. This depends on the plant's magnesium balance. Fig. 4 shows the magnesium treatment in all its options .

The operational conditions of the stages where the silicate ore/concentrate is added are the same ones already described in the integration processes I, II, III. The option of using the calcined silicate ore/concentrate is taken in accordance with the cost/benefit studies.

The processes, according to this invention, are illustrated by the non-limitative examples of practical realization hereinafter, and the following data were extracted from pilot tests and/or realizations of industrial scales:

Integration Process III:

INCREASE OF THE RECOVERY OF THE PLANT WITH THE INTEGRATION BY PROCESS III The concentrates were treated according to the flowchart of Fig. 3.

Treated amounts:

- Sulphide concentrates = 10212.332 t

- Silicated concentrates = 13291.000 t Leaching efficiency of the silicate concentrate = 94.30% Content of Zn soluble in acid = 1.79 %

Clear height in the thickening of the leached silicates concentrate = 1.4 m

Consumption of zinc powder in relation to the produced cathode = 2.94 %

Production of cathodes = 9641.430 t Problems occurred with this process:

Since the silicate concentrate is obtained by flotation, during the period in which this process was used, an expressive foam during the leaching occurred and the tanks overflew. The way to minimize such overflows was to accomplish a weak leaching, with a greater number of reactors and using floor pump to return the overflow to the origin tanks. Another solution to the problem is the Integrated Process IV.

The current efficiency (Faraday) is decreased when the total content of organic matter exceeds 3 mg/1. This parameter was controlled in the concentration Plant of the minerals of silicates, with more precise controls in the consumption of flotation or implementing the Integrated Process IV.

Integrated Process IV:

INCREASE IN THE LEACHING EFFICIENCY OF THE CALCINED

CONCENTRATES OF ZINC SILICATES AND INCREASE OF LEACHING

EFFICIENCY OF THE CALCINE FROM SULPHIDE CONCENTRATES, WITH THE INTRODUCTION OF THE CALCINED SILICATE CONCENTRATE, AT THE

END OF THE HOT ACID LEACHING.

Process IV was tested at bench, pilot & industrial plant. The obtained results are shown as follows: RESULTS OF TESTS OBTAINED IN A PILOT PLANT: Calcination of Zinc Silicate Concentrate

Fig. 5 presents the comparative results of the calcination of the concentrate at 900 °C versus raw concentrate as to the parameters loss of ignition, zinc content, carbonate content and foam formation. Fig. 5 shows that it was possible to completely eliminate the foam with the increase of the Zn content in the concentrate, from 40 % to 44% (in the calcined concentrate) and mass reduction (loss of ignition) of 20 %, referring to the elimination of the carbonates (< 0.2%) and moisture, either in bench or at industrial tests.

Effect of Calcination in the current process of Magnesium Treatment (MT)

Fig. 6 shows the results of tests of zinc selective precipitation with silicate calcined concentrate on a zinc solution with the silicates calcined concentrate on a solution of 17 g/1 of zinc and 2.1 - 2.4 g/1 of Mg

(magnesium) . The results demonstrate that, at temperatures of

90 - 95 °C and residence time of five hours, the zinc precipitates to 2.7 - 4.3 g/1, which represents an efficiency of about 80 % for zinc precipitation (17 - 4/17 x 100), and the magnesium concentration increased from 2.4 to 4.0 g/1, demonstrating an expressive capacity of magnesium purge.

Effect of Calcination on the Silicates Leaching

Fig. 7 shows that the calcination of the silicates concentrate drastically reduced the residence time, during the leaching, due to the reduction in the formation of foam, from 4 to 1 hour and 30 minutes. This rendered it possible to reduce the necessary volume to perform the leaching of the sources of zinc.

Effect of Calcination on the Purification of the Solution of Zinc Sulphate

Fig. 8 presents the results of the effect of calcination on the purification of the solutions of zinc sulphate, where there is a reduction of more than 1 % in the consumption of zinc dust in relation to the cathode produced when the solution was obtained through the calcined concentrate, from 4.12 to 2.95 %.

Leaching and filtration efficiency of the calcined ore of zinc sulphide

Fig. 9 presents the leaching and filtration efficiency of the calcined ore of zinc sulphide where it increased from 96% to 99%, according to the results obtained with the feeding of the calcined ore/concentrate of silicates, at the end of the acid leaching or beginning of the neutralization of the iron precipitation. The tests were made on benches, in volumes of 50 liters, according to the operational conditions shown in Fig. 9.

RESULTS OBTAINED IN TESTS OF INDUSTRIAL SCALE Calcination of the Silicates concentrates in Rotary Kiln Temperatures = 600 - 900 °C Residual content of carbonates = 2% or Total Carbon = 0.3% maximum

Fig. 10 presents the results of integration industrial tests where it confirms the performance of zinc selective precipitation, already shown in Fig. 6. This figure shows that the zinc content, in the liquid part of the solution was, generally, in an average of 5 g/1 when it was used a washing solution with Zn = 17 - 25 g/1 and silicate concentrate for the selective precipitation of zinc. Still in Fig. 10, the asterisks indicate that, as of day 22, 10 tanks used in the magnesium treatment were removed for cleaning, due to the constant obstruction problems in the outlet of the tanks, related to deficiency in agitation. Fig. 11 presents the results of industrial tests, when it was used the calcined silicate concentrate and the integration process of Fig. 4. The obtained leaching & filtration average efficiency ranged from 95 to 99 %, being the main impediments to keep the elevated efficiency were the low efficiency of the press-filters used for the extraction of water-soluble zinc.

Claims

1. Integration processes and gathering of ore and zinc silicate concentrates treatments with the calcine from the Sulphides Roaster characterized by joint or interlinked leachings of these several sources of zinc, their filtrations and purification in one stage of the obtained solutions, comprising four integration options:

(i) By using raw concentrates or ores of zinc silicates, from several mineral sources, which are leached together with the calcine from the roaster of zinc sulphides in the stage of Neutral Leaching.

(ii) By using raw zinc silicate ores or concentrates, from several mineral sources, interlinking with the treatment of the calcine from the Roaster of zinc sulphides, in the stages of Acid Leaching of the Ferrites and of Precipitation of Iron.

(iii) By using raw concentrates or ores of zinc silicates, from several mineral sources, interlinking with the treatment of the calcine from the roaster of zinc sulphides, in the stage of Neutral Leaching, after the silicates leaching.

(iv) By using calcined (obtained at 600 - 900 °C) of silicate concentrates or silicates ores, with selective precipitation of zinc, in the Magnesium Treatment and integration with the calcine from the Roaster of Zinc's Sulphide Concentrate, either in the stages of Neutral Leaching, Ferrites' Acid Leaching or in the Stage of Iron Precipitation.