Improvement of Beneficiation Technology for Calcium-containing Tungsten Ore

Tungsten resources are abundant and varied in China. At present, wolframite is decomposed by alkali and scheelite is decomposed by hydrochloric acid or boiled by soda. For quite a long time, experts at home and abroad generally believed that it was impossible to decompose scheelite by alkali (NaOH) in industry. Until Professor Li Honggui of Central South University put forward the hot-ball milling alkali decomposition process, which broke the convention.

However, in dealing with the mineral processing of calcium-containing tungsten ore, the method of hot-ball milling and alkali decomposition still has inconvenience in unloading operation. The amount of water used to wash out decomposed materials from ball milling is not easy to control, which can easily lead to the occurrence and extent of reversible alkali decomposition reaction of scheelite to increase, the equipment loss is large, and it is difficult to operate continuously and scale. Therefore, on the basis of Li Honggui's academic research, many scholars have made great progress in exploring, improving and perfecting this technology.

In view of the shortcomings of conventional technology, some scholars have improved and designed a method of producing sodium tungstate solution with calcium-containing tungsten ore powder as raw material in order to improve the decomposition efficiency and the utilization rate of resources, prolong the service life of equipment, adapt widely to the grade and type of minerals, filter separation efficiency, increase productivity and reduce production costs. The method is to decompose the raw ore powder with NaOH and H₃PO₄ at the required temperature and pressure. The main processes are as follows:

A.Ingredients: After grinding and fine-tungsten ore containing calcium, NaOH is added 1.4-1.6 times the theoretical amount of WO₃ in raw ore powder, H₃PO₄ is added 1.02-1.10 times the theoretical amount of calcium in CaWO₄, Al₂O₃ and NaNO₃ are added according to the weight of raw ore powder 1-6% and 0.5-1.2% respectively, and the density of slurry is adjusted to 1.55-1.60 and alkalinity to 9. 0-110 g/l;

B.Decomposition treatment: The slurry prepared above is fed into the reactor and stirred for 2-3 hours at 0.4-0.9 MPa pressure and 140-180 ℃.

C.Filtration and Separation: The slurry after decomposition is input into the filter and sodium tungstate solution is filtered; the filter residue is washed and filtered without Ca₂⁺ water, and its washing liquid is incorporated into the slurry filtrate.

The above-mentioned raw tungsten powder containing calcium includes Scheelite Concentrate powder, medium-grade scheelite powder, mixed wolframite powder and high molybdenum scheelite powder; the particle size of various powder is less than 45 micron. Na₃PO₄ can be directly used in the batching instead of H₃PO₄. It has the characteristics of scientific and accurate batching, wide adaptability range of raw materials and high effective utilization rate, low alkalinity in feed solution, weak corrosiveness to equipment, easy filtration and separation, high efficiency, good product quality, long service life of equipment, low production cost and beneficial to environmental protection.

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