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I. Introduction
China's total proven reserves of manganese ore 640 000 000 t, manganese metal reserves of 40 million t, second only to South Africa, Ukraine and Gabon, ranking fourth in the world. However, the characteristics of manganese ore resources in China are poor, fine and miscellaneous. The average manganese grade is about 21%, and the rich ore only accounts for 6.43% of the national reserves. The manganese ore type is mainly manganese carbonate ore, accounting for 73% of the total reserves. little iron and manganese oxide ore, limestone manganese and manganese ore. Since the 1980s, China imported 45% to 50% of manganese-rich ore with 25% to 30% of manganese-rich ore. In 2004, China imported manganese ore to 3.7 million tons. 90% of them are used in the metallurgical industry, and about 10% are used in the chemical industry and light industry.
In the ore dressing of manganese ore , there is no substantial breakthrough in the ore dressing of low-grade manganese carbonate ore at home and abroad. Magnetic separation is commonly used in domestic beneficiation, and the enrichment of manganese carbonate ore can only be increased by about 5%. The endowment of manganese ore in foreign countries is generally good. The flotation method is adopted for the tail sludge recovery of manganese carbonate ore. The effect is better than the magnetic separation method. The latest foreign research has adopted the electric immersion method, the Russian expert's radiometric method, the hydrothermal leaching method, etc. These are all exploratory studies on the development and utilization of manganese carbonate ore. In short, the processing of low-grade manganese carbonate ore has no mature molding technology with high recovery rate and less environmental pollution. From the development trend of manganese carbonate ore utilization at home and abroad, the development of strong selectivity, low impurity components, recycling and clean production is an important direction for the development and utilization of manganese ore resources.
Second, the experimental method
(1) Experimental instruments, reagents and raw materials
In this study, a tube type high temperature electric furnace (electronic temperature control) and a JJ200 type precision electronic balance (Changshu Shuangjie Test Instrument Factory) were used.
The ore raw material is manganese carbonate ore in a certain area of ​​Guangxi. The ore is high-silicon and low-iron manganese ore mainly composed of rhodochrosite, calcium rhodochrosite and manganese calcite . The structure is mainly composed of compact block and bean-like manganese carbonate minerals. Composition. The manganese phase composition of manganese carbonate ore and its main chemical compositions are shown in Tables 1 and 2.
Table 1 Manganese phase composition of manganese carbonate ore
Table 2 Main chemical constituents of manganese carbonate ore
Reagents used include: ammonium chloride (technical grade), disodium hydrogen phosphate (AR) phosphate, silver nitrate (analytical grade), ammonium persulfate (AR), ferrous ammonium sulfate (AR), benzoguanamine o Aminobenzoic acid (analytical grade) and the like.
(two) experimental principles and methods
In this study, ammonium chloride roasting was used to decompose, converting manganese into water-soluble manganese chloride, and then leaching manganese chloride with hot water. The response is as follows:
The manganese carbonate ore is mixed with ammonium chloride and then placed in a muffle furnace for firing. The calcined mixture was leached with hot water and filtered. The manganese content in the leachate was analyzed to calculate the leaching rate of manganese. The effects of calcination temperature, ammonium chloride dosage and calcination time on manganese leaching rate were investigated.
The volumetric method was used to analyze the manganese content in the leachate, and then the manganese leaching rate was calculated. Take appropriate amount of the test solution in a 250ml Erlenmeyer flask, add 15ml of 10% disodium hydrogen phosphate solution, 5ml of 1% silver nitrate solution, 20ml of 15% ammonium persulfate solution, and dilute with water to about 150ml. Heat and boil until large bubbles appear, then keep it for 5-7 minutes, and cool to room temperature with running water. Then, titrate to a light red color with a standard solution of ammonium ferrous sulfate, and then add 4 to 6 drops of 0.2% benzoanthranilic acid indicator, and then slowly titrate until the solution turns from purple to bright green, which is the end point. The leaching rate of manganese (Mn%) is calculated as follows:
Where: mass of manganese in m-ore (g);
m 0 - the molecular weight of manganese;
M-ferrous ferrous sulfate standard solution concentration (mol / L);
Volume of volume consumed by V-ferrous ammonium sulphate titration (ml);
V 1 - total volume of test solution (ml);
V 2 - the volume of the test solution (ml)
The process of enriching and recovering manganese from low-grade manganese carbonate ore in this experiment is shown in Figure 1.
Third, the results and discussion
For the convenience of research, the best process of the roasting process was first investigated. The experiment was carried out in a muffle furnace. A certain amount of manganese carbonate ore was mixed with solid ammonium chloride. After roasting for a certain period of time, the calcine was cooled and leached with hot water. , filtering, analyzing the concentration of manganese in the filtrate, so that the manganese leaching rate can be calculated.
Figure 1 Process for enrichment of manganese concentrate from low-grade manganese carbonate ore
(1) Effect of chlorination temperature
Each time 10g of manganese carbonate ore and 12g of ammonium chloride were weighed and mixed uniformly, and calcined at different temperatures for 1h, the manganese content in the filtrate was analyzed. The effect of calcination temperature on manganese leaching rate is shown in Fig. 2.
Figure 2 Effect of calcination temperature on manganese leaching rate
As can be seen from Fig. 2, in the range of 300 ° C to 450 ° C, the recovery rate of manganese gradually increases as the reaction temperature increases. When the temperature is 450 ° C, the recovery of manganese reaches 95% or more. In the range of 500 ° C ~ 600 ° C, the leaching rate of manganese decreases with increasing temperature. The reason why the leaching rate of Mn fluctuates above 500 °C may be due to the decomposition of manganese carbonate at high temperature, and the product valence is unstable, and it is easily oxidized by oxygen in the air, while the high-valent manganese oxide is not easily chlorinated. , causing a decrease in the leaching rate of manganese. Therefore, the optimum chlorination temperature is 450 °C.
(two) the impact of ammonium chloride dosage
10 g of manganese carbonate ore was weighed, and different amounts of ammonium chloride were added and calcined at 400 ° C and 450 ° C for 1 h. The relationship between the leaching rate of manganese and the amount of NH 4 Cl is shown in FIG. 3 . It can be seen from Fig. 3 that when the amount of NH 4 Cl is insufficient, the leaching rate of manganese increases rapidly with the increase of the amount of NH 4 Cl. When the amount of ammonium chloride is 1.2 times the mass of manganese carbonate ore, the leaching rate of manganese No longer significantly increased. Thereafter, if ammonium chloride is continuously added, the leaching rate of manganese is also substantially maintained at about 98%. From the comparison of the two sets of temperature conditions, at a high temperature of 450 ° C, the amount of ammonium chloride used is 1 times the mass of manganese carbonate ore, the leaching rate of 98% can be achieved, and the optimum chlorination at 450 ° C The amount of ammonium used is: ammonium chloride / ore = 1.
Figure 3 Effect of ammonium chloride dosage on manganese leaching rate
(3) Influence of chlorination roasting time
10 g of manganese carbonate ore was added to 15 g of ammonium chloride, and calcined at 400 ° C and 450 ° C for different times. The leaching rate of manganese with time is shown in Figure 4. As can be seen from Fig. 4, the chlorination roasting time is preferably 1.5 h, and the leaching recovery rate of manganese can reach 95% or more.
Figure 4 Effect of roasting time on manganese leaching rate
Through the above experiments, it can be determined that for manganese carbonate ore treated with ammonium chloride, the optimum calcination conditions are: calcination temperature is 400 ° C ~ 450 ° C, calcination time is 1 ~ 1.5 h, ammonium chloride dosage is NH 4 Cl / carbonic acid Manganese ore = 1.0 to 1.2. Under the best conditions, the leaching rate of manganese can reach more than 95%.
(IV) NH 4 Cl recycling experiment
Weighing 10 g of manganese manganese ore from a manganese ore in Guangxi and 12 g of multiplexed NH 4 Cl obtained by evaporation and crystallization were ground and mixed uniformly in a mortar, placed in a 50 ml quartz burning boat, and calcined at 450 ° C for 1 h in a tube furnace. The gas generated during the roasting process is introduced into the last leachate by vacuum. The manganese in the leachate absorbs the ammonia gas and the carbon dioxide produced by the roasting to form a precipitate. After the calcination is completed, the absorption liquid is filtered, and the Filter cake is dried to obtain a manganese concentrate; 5 cycles In one group, the filtrate obtained by 5 times of absorption is concentrated by evaporation, and 5 g of ammonium hydrogencarbonate is added to precipitate the manganese completely, and further crystallization is carried out by evaporation to obtain an ammonium chloride solid, which can be used as an ingredient for the next baking. The results obtained by the three sets of experiments are shown in Table 3.
Table 3 Results of enrichment cycle of low-grade manganese carbonate ore
Fourth, the conclusion
The manganese in the manganese carbonate ore is enriched and recovered by ammonium chloride roasting. The optimum conditions for the calcination are that the amount of ammonium chloride is 1.0 to 1.2 times the weight of the manganese carbonate ore, and the chlorination reaction temperature is 400 ° C to 450 ° C. The time is 1 to 1.5 hours. Under these conditions, the leaching rate of manganese can reach more than 95%. Cyclic experiments show that the decomposition of ammonia and carbon dioxide in the roasting process can precipitate the manganese chloride solution and obtain manganese concentrate (manganese content is more than 50%). The recovery rate of manganese can reach more than 90%. The loss of manganese is mainly in the discharge. In the slag, the unrecovered manganese in the absorption precipitate remains in the filtrate, evaporates and enters the recovered ammonium chloride, and accumulates in the system. The process recovers ammonium chloride by evaporating the filtrate of the absorption liquid, and as a roasting ingredient, the whole system can form a closed circuit cycle, and no waste gas and waste water are generated except for a small amount of waste residue discharge. Therefore, it will not pollute the environment and is a new green technology worth developing.
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