Treatment of low grade molybdenum ore by electrooxidation

Electrooxidation treatment of low-grade molybdenum ore is a new technology developed in recent years. Invented by the US Mines Bureau and expanded on the basis of small tests. Other countries in the world are also conducting in-depth research and generally believe that this is a promising approach. At home, it is understood that no research has been conducted in the past.
Mineral production showed abroad, since the influence of molybdenum minerals insert some unevenness of a particle size distribution of the impurity element, the dressing process always enter a part of the ore concentrate, the concentrate quality impact; if into the tailings, the influence The recovery rate of molybdenum. Therefore, how to deal with this part of the mine has always been a subject to be studied.
Beijing Research Institute of Mining by electro-oxidation of the two JINDUICHENG in low grade ore dressing plant extraction of a production of ammonium type challenge tests showed that when the feed containing 1.30% of Mo, the leaching rate of 96 to 98 %, the extraction rate is about 99%, the obtained ammonium molybdate contains Mo more than 60%, and the total recovery of Mo is about 90%.
1. The ore-bearing nature of the ore is the low-grade medium ore of the Jincheng Second-selection Plant (selected 1 tail + separation sweep 1 fine). Its main chemical composition (%): Mo1.30, Cu0.78%, Fe 13.30, Pb 0.05, Zn 0.16, CaO 2.46, MgO 1.45, S 11.85, K ₂ O 4.11, Na ₂ O 0.72, C 0.40, WO ₃ 0.0038, Sn 0.0052, Bi 0.0085, As 0.00019, P 0.11, Re<0.0005.
Generally the various content (%) metal ores: 19 pyrite, magnetite 3.0, 2.30 brass ore, molybdenite 2.15, in addition there are small amounts of sphalerite, galena, sulfur, bismuth, copper, lead, Needle bismuth lead ore.
Approximate content of the various gangue minerals (%): 34.0 quartz, sericite 15.0, 13.0 orthoclase, chlorite 5.5, 4.0 fluorite, calcite 1.0 other 0.4.
The state of occurrence of molybdenum in each fraction of the raw material is as follows.

It can be seen from the above table: (1) The molybdenum oxide in the feedstock is small, and the oxidation rate is only 0.775%. The oxides of molybdenum are mainly high-iron molybdenum and molybdenum. (2) The degree of dissociation of coarse-grained monomers is low, and there are more molybdenum inclusions in the continuous body and gangue of molybdenite and gangue. As the particle size decreases, the degree of dissociation of the monomer increases, and the protoplast and inclusion molybdenite decrease, and the -44μ particle size dissociation is better. [next]
2. Mechanism of action Electrooxidation actually involves two processes: (1) electrolytic NaCl aqueous solution to form NaClO oxidant; (2) NaClO oxidized molybdenum ore. Both steps were carried out with constant stirring in a reactor-stirred tank, and no positive and negative grade products were precipitated.
The reaction formula of sodium hypochlorite oxidized molybdenum ore:

MoS ₂ +5ClO ^- +40H ^- -→ MoO ₄ ⁼ +S ₂ O ₂ ^- +5Cl ^- +2H ₂ O (1)
4ClO ^- +S ₂ O ₃ ⁼ +20H ^- —→ 2SO ₄ ⁼ +4Cl ^- +H ₂ O (2)
MoS ₂ +9ClO ^- +60H ^- -→ MoO ₄ ⁼ +9Cl ^- +2SO ₄ ⁼ +3H ₂ O (3)

NaClO is formed by electrolyzing an aqueous solution of NaCl. When graphite is used as the anode and cathode, the reaction is:

Anode: 2Cl ^- —→ Cl ₂ +2e ^- (4)
Cathode: 2H ₂ O+2e ^- —→ 2OH ⁺ +H ₂ (5)

The Cl2 and OH- formed in the solution combine to form OCl-, and the reaction:

2OH ^- +Cl ₃ —→ OCl ^- +H ₂ O+Cl ^- (6)

If the ore contains barium , sodium hypochlorite will simultaneously oxidize the barium, and its reaction:

^{_{Re 2 S 7 + 28ClO - +}} 160H - - → 2ReO 4 - + 28Cl - + 8H 2 O + 7SO 4 = (7)

It can be seen from the formula (3, 7). After the reaction of ClO ^- formed by electrolysis of the NaCl aqueous solution with MoS ₂ or Re ₂ S ₇ , Cl ^- is formed again. Therefore, the leaching process itself does not consume NaCl. Therefore, after leaching, the slurry is filtered, and it is filtered back to electrolysis to regenerate ClO ^- . The loss of NaCl is limited to the portion of the filter that is carried away.
From the oxidation rate, when the solution contains NaClO less than 30 g / liter, and the free state alkali is less than 20 ~ 30 g / liter, the molybdenum ore is oxidized faster, and the copper and iron sulfides at 20 ~ 40 ° C The oxidation rate is smaller than that of the mine. Moreover, the electrooxidation process produces NaClO while reacting with MoS ₂ , and almost no excess NaClO reacts with other metal minerals. Therefore, the method is selective for the oxidation of molybdenum ore, and the content of other metal impurities in the leachate is low.
3. Test method and results The raw material used for each test was 90 g, containing 1.3% of Mo, and was slurried with a NaCl aqueous solution, and leached in a stirred tank. After leaching, the slurry is filtered, and the slag is rinsed with 1% Na ₂ CO ₂ water (temperature: 30 to 40 ° C), and then rinsed with water (temperature 30 to 40). The leaching rate is calculated based on the amount of Mo contained in the slag. The pulp pH was adjusted with Na ₂ CO ₃ . Since the Re contained in the feed is too low, the recovery of Re is not considered.
The principle process is shown in Figure 1. The schematic diagram of the leaching test device is shown in Figure 2. [next]

Figure 1


Figure II
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When directly oxidizing molybdenum oxide of chloric acid in NaCl slurry, there are many influencing factors. In the research process, the main factors such as NaCl concentration, slurry concentration, pulp pH, slurry temperature, grinding fineness, leaching time and current density are studied. factor. It is briefly described as follows:
(1) NaCl concentration When the current density is the same, the higher the NaCl concentration, the more NaClO is produced. When the NaCl concentration is 5-15%, the amount of NaClO produced is relatively close. As the NaCl concentration increases, the amount of molybdenite oxidation increases. When the NaCl concentration reaches 10%, the leaching rate of Mo is 97.87. %, when the concentration of NaCl is further increased, the leaching rate of Mo is almost unchanged.
(2) Grinding fineness Because the feeding material is the low-grade medium ore of Jinduicheng Second-selection Plant, the coarse-grained medium-sized calcareous ore has more continuum and inclusions, and the dissociation degree is only 63%. Zhonghui molybdenum mine is fully dissociated and needs to be reground. When the feedstock is not ground (63%-400 mesh), the leaching rate of Mo is 92.985. When the feed is milled to 89%-400 mesh, the leaching rate of Mo is 97.78%, which is higher than that when not grinding. The rate is nearly 5%. If the fineness continues to increase, the leaching rate of Mo increases little.
(3) Current density In a solution having the same NaCl concentration, the concentration of ClO ^- produced by electrolysis mainly depends on the current density. The higher the current density, the greater the concentration of ClO ^- produced. The ClO ^- concentration determines the oxidation rate of molybdenite. As the current density increases, the leaching rate increases accordingly. When the current density is 800 amps/m2, the Mo leaching rate is 97.08%. If the current density is further increased, the Mo leaching rate increases little.
(4) pulp pH
In the process of directly electrolyzing NaCl to leaching molybdenum ore from the slurry, sodium carbonate is continuously added to the slurry to control its range in the range of p5-6. When the pH value is lower than 5 or higher than 7, the leaching rate of Mo decreases, and the leaching rate of the surface ju increases. When the pH is 5-6, other major metal ions, such as Cu and Fe, are in a precipitation state, so other metal impurities are less in the leachate. When the pulp pH is 6, the Mo leaching rate is 97.78%.
(5) Slurry temperature The reaction between NaClO and MoS ₂ is an exothermic process, so as the reaction proceeds, the temperature of the slurry gradually rises. When the slurry temperature is 40 ° C, the Mo leaching rate is relatively high. When the slurry temperature is relatively high, NaClO begins to decompose and precipitates oxygen. Some of the precipitated oxygen ran away without participating in the reaction, so that the amount of NaClO was much higher than the theoretical value of the oxidized molybdenite. Therefore, when electrolytic leaching, the slurry temperature should generally be below 40 °C. However, in order to keep the temperature of the slurry below 30 °C, it is necessary to take measures to reduce the temperature. Therefore, the temperature of the slurry is suitable at 30-40 °C. When the temperature of the slurry is 30 °C, the leaching of Mo is 97.08%.
(6) Concentration of pulp The concentration of pulp can determine the concentration of Mo ion and the amount of treatment in the leachate, and has a great influence on the leaching rate of Mo. When the slurry concentration is greater than 20%, the Mo leaching rate is greatly reduced. When the slurry concentration drops to 10%, the leaching time can be doubled, and the leaching rate of Mo still reaches 98.42%. However, considering the comprehensive consideration, the slurry concentration of 20% is more suitable.
(7) Leaching time The leaching time depends mainly on the magnitude of the current density. As the current density increases, the leaching time can be correspondingly reduced. When the Mo leaching rate is 97% or more, when the current density is 400 amps/m ² , leaching is required for 4 hours; when the current density is 800 amps/m ² , leaching is required for 3 hours. Therefore, the leaching time should be determined according to the selected current density.
4. Comparison with sodium hypochlorite solution leaching method
In order to compare the electrooxidation method with the direct leaching of molybdenite with hypochlorous acid solution, the leaching time and the leaching solution electrolysis regeneration ClO-test were carried out with sodium hypochlorite. In order to examine the effect of the immersion liquid returning, a small test of sodium hypochlorite solution leaching - electrolytic leaching - solvent extraction - electrolytic leaching was carried out. The principle process is shown in Figure 3. [next]

Figure III

It can be seen from the above figure that the leaching rate of Mo is 98.09% when the sodium hypochlorite solution is directly leached; the leaching of Mo is 97.12% in the first electrolytic leaching, and 0.97% when leaching with the sodium hypochlorite solution; the second electrolytic leaching The leaching of Mo was 96.51%, the leaching with sodium hypochlorite solution was 1.58%, and the first electrolytic leaching was 0.61%. The results were not much different, and the indexes were similar to those of the NaCl solution. In order to ensure the leaching rate of Mo, when the leachate is returned to the product multiple times, a small amount of sodium hypochlorite solution or NaCl should be added to each electrolytic leaching to compensate for the loss of NaCl.
In short, the electro-oxidation method is basically the same as the direct leaching with sodium hypochlorite solution, but the electro-oxidation method can make the leachate obtained by the two-way method produce hypochlorite and return it to use, and the economic effect is obvious.

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