Process Study Of Scheelite Floatation Enrichment And APT Preparation Through Complex Acid Method

Comprehensive utilization of low grades scheelite is of great significance to sustainable development of tungsten industry, resource guarantee and efficient use. The properties of scheelite decide that it is difficult to remove gangue from scheelite. Nowadays, new separation technology is focusing on the new flotation reagents, but it takes insufficient account of the effect on the environment. On the other hand, the digest methods of scheelite have to face to some thermodynamic and kinetic problems. In this work, scheelite floatation enrichment, complexation acid leaching, leaching solution treatments and purifications process are studied. Ammonium paratungstate (APT) is produced by evaporation and crystallization with the cleaning solution. The experimental study is focus on the technology parameters and elucidating the process mechanism. A new technology is proposed to achieve the high-efficiency utilization of scheelite resource.In the part of scheelite floatation, high temperature and ambient temperature floatation methods are used, and effecting rules of each factor are studied using environmental friendly reagents. The results show both methods can achieve scheelite enrichment effectively and the highly grade scheelite concentrate is obtained. The high temperature method has good adaptability of raw ore, and 65% grade scheelite concentrate is enriched by high temperature cleaning floatation. On the other hand, the ambient temperature floatation has the advantages of environmental friendly and low energy consumption. Calcium oxide and sodium carbonate are used as the depressant,45% grade scheelite (recovery rate 65%) up to 65% grade scheelite concentrate (recovery rate 35%) is obtained.Then, in the part of complexation leaching, the synthetic scheelite and scheelite concentrate are used for the leaching process kinetics’ experimental research. The results show leaching process accords with solid-liquid multiphase shrinking core model. The reaction rate is controlled by interface reaction, and the apparent activation energy is 60.65kJ/mol, which calculated according to the Arrhenius equation.The scheelite concentrate used as raw material, the influence rules of the factors are tested and the sutructure type of the leaching liquor is studied. The results show that the reaction temperature, reaction time, hydrochloric acid concentration and W/P mole ratio can affect tungsten leaching rate obviously. The optimum technological condition is stirring speed 1000r/min, temperature 80℃, hydrochloric acid concentration 2.16mol/l, W/P mole ratio 7:1, reaction time 3h, the leaching rate is more than 98%. The leaching solution is detected by means of an IR spectra, the results show the tungsten salt is Keggin structure salt H3[PW12O40].According to the experimental results, process parameters can be optimized, the hydrochloric acid concentration and reaction temperature are lower than the traditional acid method under the same leaching rate level. It shows the new leaching method can reduce the material and energy consumption, and is more environmentally friendly.The study of treatment processes of complex leaching liquor is still almost a blank, and the technology of APT produce by comlex leaching liquor has a practical significance. In the part of leaching solution treatment and purification process, based on the characteristics of the complexation leaching solution, the novel two stage technology is presented. First of all the tungsten in the solution is precipitated and the (NH4)3[PW12O40]xH20 available, secondly the precipitate was dissolved by adding ammonia. In the precipitation stage, the sedimentation velocity is slow and the ultrasound wave uses as external fields to accelerate the settlement processes. Under the condition of temperature 20℃, ultrasound frequency 20kHz, load time 3 minutes, ultrasound power 90W, the sedimentation time would be shortened more than 20%, and the mechanism is revealed according to the experimental results. The solid (NH4)3[PW12O40]·xH2O is size mixing by adding deionized water and dissolved via dropping concentrated ammonia until solution clearly. Fe is removed by oxidation-hydrolysis method; P is removed under the condition:Mg2+ concentrate 0.2mol/l, pH value 8.5-9, reaction time 30 minutes, 1.1 times theoretical value dosage of magnesium; Mo is removed under the condition:pH value 8-9, sulfuration reaction 2h, n(S)/n(Mo) ratio=16, precipitation reaction 1h, n(Cu)/n(Mo)=3. At last, the crystal product (NH4)10H2W12O42·4H2O is obtained after evaporation and crystallization. The tungsten content and the three main impurities content of the solid APT product can reached the national standard requirements. In this work a novel scheelite comprehensive utilization technology is studied, which can decompose the scheelite concentrate by complexation leaching and prepare APT with low energy and matieral consumption.