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I. Utilization status of low grade pyrolusite/foreign manganese nodule ore and manganese sulfide ore
Methods manganese sulphate of manganese ore with a soft braking, only the reduction roasting - pickling process with a reducing agent, and a direct acid leaching. Both methods require calcination or a reducing agent (mineral), which not only increases the production cost of manganese sulfate, but more importantly wastes a lot of valuable non-renewable energy or mineral resources.
China's soft manganese ore is rich in ore, most of which are lean ore with MnO 2 content less than 40% (mass fraction). The ore is reduced in economical efficiency by reduction roasting and acid leaching. Direct acid leaching conventional methods pyrite method, ferrous sulfate method, bacterial leaching method or the like, with processing effects are not.
Sea manganese nodules distributed in the ore is a kind of multi metal tuberculosis ocean floor, MnO 2 content of 20% to 25% (mass fraction), the major mineral water Manganese (Mn 2 O 3 · H 2 O) and partial manganate ore (MnO 2 · nH 2 O) , can be attributed to poor oxide ore a class principle, which also contain copper, nickel, cobalt and other valuable metals, is an important source of this century strategic metals manganese, copper, nickel, and cobalt. Due to its low water content and low manganese content, no breakthrough has been made in its smelting technology. The hydrochloric acid leaching method, ammonia leaching method and bacterial leaching method are reported, mostly in the experimental stage due to economic benefits, environmental pollution, etc. The problem is that it does not have industrial application conditions.
Manganese sulphide ore is another widely distributed primary manganese ore. When it contains a small amount of silver , it becomes a silver-manganese ore. Due to its low manganese content and difficult handling, it is usually retained as an off-balanced ore (another silver-manganese ore is silver-containing soft. Manganese ore, which is essentially an oxidized ore containing silver-manganese sulfide ore, can be considered to be used in low-grade pyrolusite. However, since it can be directly acid leached, it does not need to be subjected to reduction roasting treatment first, and the leaching process is relatively simple; at the same time, since the manganese sulfide ore usually contains a trace amount of silver, the silver in the leaching residue is initially enriched, and can be extracted from silver or sold as silver-containing slag. Therefore, many small mines and enterprises use manganese sulfide ore as raw material, and through the simple acid leaching method with dilute sulfuric acid, firstly produce manganese sulfate and then extract silver from the leaching residue, which has certain economic benefits.
However, this process has a fatal drawback, i.e. acid leaching process produces a large amount reached 300mg / L or more hydrogen sulphide gas, very poor working conditions, but also causes serious environmental pollution.
The conventional method for treating hydrogen sulfide gas pollution is lye absorption method, but this method is complicated in equipment, large in investment, high in processing cost, low in concentration of absorbing liquid, and difficult to recycle, which is difficult for general enterprises to accept. Some enterprises use high-grade pyrolusite [w(MnO 2 )>60%] to directly lease together with manganese sulfide ore, but no matter how high the price of high-grade pyrolusite is, and when the manganese sulfide ore is directly put into acid leaching, no matter how many The strong oxidant, the first to produce is the hydrogen sulfide gas, so the direct leaching of manganese sulfide ore with high-grade pyrolusite is actually not feasible.
2. Direct leaching of low grade pyrolusite/foreign manganese nodule ore and manganese sulfide ore
In order to achieve the purpose of directly leaching low-grade pyrolusite/ocean manganese nodule ore and manganese sulfide ore to obtain manganese sulfate without roasting, no consumption of reducing agent (mineral), and no hydrogen sulfide gas, two-step circulation leaching can be used. method. The Chinese invention patent CN1465723A provides the first step to solve this problem - reduction leaching (acid leaching). Characterized in that patent is: low-grade manganese ore (ore or sea manganese nodules) and concentrate sphalerite (ZnS) simultaneously, directly leach in dilute sulfuric acid to obtain a solution of ZnSO 4 and MnSO 4:
FeSO 4 is used as a catalyst in the reaction to accelerate the decomposition of low-grade pyrolusite (or ocean manganese nodule) and sphalerite concentrate.
ZnS is prone to ionization in liquid phase conditions, in lower acidity, and in the presence of oxidants:
The concentration of S 2 - in the solution depends on the acidity, and the smaller the acidity, that is, the higher the pH, the greater the concentration of S 2 - . When the oxidant is sufficient, S 2 - will be further oxidized to a high-valence state through this liquid phase route:
This is a homogeneous liquid phase oxidation reaction with a large thermodynamic driving force. In the presence of oxidant, the intermediate products SO 3 2 - and HSO 3 - are difficult to accumulate to a large concentration and will be rapidly oxidized to SO 4 . 2 - , that is to say, there will be no H 2 S and SO 2 gas generation. Experiments have shown that these gases are not formed in the reaction.
The second step - metathesis leaching (neutral leaching): the first step of reducing the leaching solution (MnSO 4 + ZnSO 4 ), after the iron removal treatment, the manganese sulfide concentrate powder is directly added to the purified manganese-zinc mixed solution Convenient and economical completion of manganese and zinc separation:
Since the solubility product of ZnS (Ksp = 1.2 × 10 -24 ) is much lower than MnS (Ksp = 1.4 × 10 -15 ), this reaction can be carried out thoroughly, and its thermodynamic conditions have spontaneous reactions at normal temperature and pressure. Possible. In order to accelerate the progress of the reaction, the reaction temperature can be raised. The experiment proves that when the temperature is ≥85 °C, the solution is in a self-boiling state, and the reaction proceeds very quickly, and can be completed in a few minutes. Since the reaction is carried out in a neutral solution, no H 2 S gas is produced at all, and sulfur and manganese in the manganese sulfide ore are fully utilized.
The secondary leaching greatly increases the production of manganese sulfate and has a relatively high economic benefit. The precipitated ZnS can be directly returned to the reduction leaching of low-grade pyrolusite/ocean manganese nodule ore without water washing. This newly formed ZnS has greater reactivity than zinc concentrate and can further accelerate the rate of reduction and leaching. And can make the reaction more thorough.
Thus, the first step of reduction leaching (acid leaching): using a low-grade pyrolusite/ocean manganese nodule ore and ZnS under the catalysis of a soluble iron salt, directly leaching in dilute sulfuric acid to obtain a zinc-manganese mixed solution; Metathesis leaching (neutral leaching): Separation and purification of the zinc-manganese mixed solution with manganese sulfide concentrate to precipitate ZnS; ZnS is returned for a new round (first step) reduction leaching. As a result of such repeated cycles, low-grade pyrolusite/ocean manganese nodule ore and manganese sulfide ore are directly leached to obtain manganese sulfate, and the useful elements Mn, S, O, and Ag in the two minerals involved in the reaction are fully utilized. However, ZnS is only recycled, and it is basically not consumed. In fact, it is equivalent to directly leaching low-grade pyrolusite/foreign manganese nodule mine with manganese sulfide concentrate. ZnS can be obtained by reacting ZnSO 4 with manganese sulfide concentrate:
Third, the process flow (see Figure 1)
Figure 1 process flow chart
In principle, manganese sulfide ore can be used for neutral leaching, but its manganese content is low, the quality is poor, the reaction is slow, and the slag amount is large. The effect is not as good as using the manganese sulfide concentrate enriched by ore dressing , and the zinc sulphide concentrate zinc is used to obtain ZnS with less slag content, which is more suitable for re-leaching.
In the process of neutral leaching of precipitated ZnS, a slight excess of manganese sulfide concentrate is required to precipitate the zinc as completely as possible, so that a small amount of residual manganese sulfide ore is mixed with the precipitated ZnS. Returning to the first step of reducing leaching, a small amount of H 2 S gas is initially produced. The solution to this problem can be a small improvement in the process: the ZnS precipitate mixed with a small amount of manganese sulfide ore is first returned to the new purified zinc-manganese mixed solution to remove excess manganese sulfide ore. And then used for a new round of reduction leaching.
When the manganese sulfide ore contains manganese carbonate ore, during the metathesis leaching (neutral leaching), the manganese carbonate ore is mixed with the precipitated ZnS. When returning to a new round of reduction leaching, the remaining manganese sulfide ore will be fully utilized. Does not affect the reduction leaching.
When silver sulfide is contained in silver sulfide, it is called silver-manganese ore. The reference describes the method of leaching silver-manganese ore by high temperature, high acid and high oxidant (high grade pyrolusite). The manganese leaching rate is more than 98%, but There is no mention of whether H 2 S gas is produced during leaching, and the hazard of H 2 S gas and its treatment. In the process of metathesis leaching (neutral leaching), silver is mixed with precipitated ZnS. When returning to a new round of reduction leaching, ZnS is dissolved, and silver is enriched in reducing leaching slag, which can be extracted from Silver does not cause any waste of silver resources, and this method of using silver-manganese ore does not produce H 2 S gas, which is more convenient, environmentally friendly and economical than all existing methods.
Fourth, conclusions and experimental examples
The technical method enables the useful elements Mn, S, O, Ag, etc. in the low-grade pyrolusite/ocean manganese nodule ore and manganese sulfide concentrate to be fully utilized in a single cycle process. Moreover, the two minerals are directly leached, eliminating the roasting process, and no H 2 S gas is generated during the leaching process, which not only makes full use of limited resources, but also greatly reduces greenhouse gas emissions and environmental pollution of other harmful gases. , optimize the process operating conditions, and will greatly reduce the production cost of manganese sulfate, with significant economic and environmental benefits, in line with the principle of sustainable development.
The manganese sulfide concentrate used in the experiment was taken from Liancheng manganese ore in Fujian Province, with a particle size of less than 106 μm, a mass fraction of Mn of 43%, an S mass fraction of 25%, and an actual MnS mass fraction of about 65%. The manganese sulfide concentrate is added to the purified zinc-manganese mixed solution in a theoretically calculated value of 110%, boiling from 5 to 10 minutes at 90 ° C, and the pH of the reaction is 5.5 to 6.5. The Zn mass fraction in the solution was analyzed to be 0.1%; the leaching residue was leached again with a new purified zinc-manganese mixed solution, leached at 40 ° C for 60 min (or boiling at 5 ° C for 5 to 10 min at 85 ° C), and analyzed for leaching The medium MnS mass fraction was 1.2%.
There is no hydrogen sulfide gas generated during the reaction. The experimental results show that the precipitation rate of ZnS and the utilization rate of MnS are more than 99%, the leaching effect is very good, and the equipment is simple, the process conditions are loose, and the energy consumption is low, which is suitable for industrial production. use.
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