Study on Preparation of Ammonium Molybdate from Amorphous Molybdenum Ore

Abstract: Molybdenum ore is used as a raw material in some places in China. It has been found that molybdenum exists in the form of amorphous sulfide. The general beneficiation and the wet extraction methods described in the literature cannot meet the requirements of industrial application. The ammonium molybdate product was prepared by directly converting the molybdenum into a molybdenum-containing solution by oxidizing roasting, sodium carbonate solution, high temperature and high pressure leaching, and adding a certain amount of solid ammonium chloride to heat and precipitate ammonium molybdate. The optimum process technical parameters are selected through conditional tests. The molybdenum content in the ammonium molybdate is greater than 55% (mass fraction), and the recovery of molybdenum is greater than 90%.
Key words: amorphous molybdenum ore; ammonium molybdate; ammonium chloride.
1 Raw material analysis results of material components : ω / (SiO ₂ ) = 21.77%, ω / (K ₂ O) = 1.04%, ω / (Fe ₂ O ₃ ) = 15.96%, ω (Na ₂ O) = 0.22% , ω(Al ₂ O ₃ )=8.28%, ω/(TiO ₂ )=0.33%, ω/(CaO)=7.28%, ω/(MgO)=2.10%, ω(S)=19.48%, ω( P) = 0.16%, ω / (Mo) = 4.32%, ω (Ni) = 3.14%, ω / (Mn) = 0 0.045%, ω / (C) = 13.00%.
Ore by X-ray diffraction pattern analysis, no molybdenum (Ni) and mineral spectral peak, only sulfur-containing mineral pyrite (iron disulfide), mass fraction of 14%, which in terms of sulfur content of total mass 7.5%, and the chemical analysis results of the ore indicate that the sulfur content is as high as 19.48%, which is obviously unbalanced. According to this judgment, molybdenum (nickel) exists in the form of an amorphous sulfide. Other major mineral components of the ore are: quartz , carbon, dolomite, mica , siderite, kaolinite, etc.
2 Principle Process The formulation of the original ore has a low molybdenum grade, high sulfur and carbon content, and has been attempted to be enriched by flotation or re-floating. Because it does not crystallize to form an independent mineral, it is closely symbiotic with carbon and has an inlaid grain size. It is extremely fine and cannot be effectively separated from other minerals, making the crystal position and recovery of the concentrate extremely unsatisfactory. Thus, this study hydrometallurgical extraction process wherein the molybdenum. The ore is directly oxidized and calcined, and then the sodium molybdate product is prepared by leaching with a sodium carbonate solution at a high temperature and high pressure, and then separating the molybdenum in the leach solution with ammonium chloride. The principle process is: raw ore→crushing→grinding→oxidation roasting→sodium carbonate solution leaching→ammonium chloride precipitation→filtration washing→drying→ammonium molybdate product.
The literature introduces the process route of preparing ammonium molybdate with low-grade molybdenum concentrate. The preparation process is carried out under normal pressure and is a well-crystallized molybdenum ore raw material. On the basis of the literature, the effects of sodium carbonate dosage, leaching reaction time and leaching temperature (pressure) on leaching rate were studied, and the optimal leaching conditions were determined based on this, and ammonium molybdate was prepared by ammonium chloride. Process technical indicators. [next]
3 Test results and analysis 3.1 Sodium carbonate solution leaching test Test equipment: l 000 W adjustable electric furnace; speed control electric mixer; 200 mL stainless steel reactor, homemade; temperature control oven.
Reagents: sodium carbonate, chemically pure.
Main reaction:
2MoS ₂ +7O ₂ =2MoO ₃ +4SO ₂ ↑
MoO ₃ +Na ₂ CO ₂ =Na ₂ MoO ₄ +CO ₂ ↑
3.1.1 Sodium carbonate dosage test The test conditions are: liquid-solid mass ratio 2:1, temperature 100 ° C, time 1 h. Take 100g of the calcined sample, grind to 52 μm, add different amounts of sodium carbonate, add the amount of mass to the solid ore, two-stage leaching, the same amount of the first and second addition, add 200 mL Water, heated to 100 ° C, stirred for 1 h, cooled, filtered and washed, and the slag was dried to analyze the molybdenum content. The molybdenum content of the sample after immersion roasting was 4.07% (mass fraction), and the test results are shown in Table 1. It can be seen from Table 1 that when the amount of sodium carbonate is 50%, the leaching rate is relatively prominent, but the dosage is too high and uneconomical. In general, the leaching effect under normal pressure is not ideal, but it provides a certain reference for high temperature and high pressure leaching tests.

3.1.2 Leaching time test Test conditions: liquid-solid mass ratio 2: l, sodium carbonate dosage 40%, temperature 100 °C. When the leaching time was 1 h, 2 h, 3 h and 4 h, the molybdenum content (mass fraction) of the primary leaching slag was 1.40%, 1.6l%, 1.54% and 1.68%, respectively. The results showed that the leaching time had no significant effect on the leaching effect, and it was suitable for 1 h.
3.1.3 Leaching temperature (pressure) test
Test conditions: liquid-solid mass ratio 2: l, leaching time lh, sodium carbonate dosage 30%, the results are shown in Table 2. The results show that the closed static leaching rate at 160 °C is much higher than the dynamic leaching rate at normal pressure, which exceeds the expected index of 90%. Considering that the temperature is too high, the equilibrium pressure in the state of the reaction is also increased, and the requirements on the equipment are more stringent, and the reaction temperature is preferably 160 ° C, and the pressure at the state is about 606 kPa.

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