Technology of ion exchange has brought significant technical progress in China's tungsten smelting, but it also has some defects at the same time. Especially wastewater generated from ion exchange has gradually become prominent with the environmental issues becoming more important. It mainly comes out in the following aspects:
1. Low feed concentration, and the large water consumption standout;
2. The low unit handling capacity of strong basic resin makes the small work of exchange capacity;
3. Wastewater is in large amount and difficult to deal with.

Ion exchange method base on Weak-base anion-exchange resin to prepare ammonium paratungstate is proposed in this paper. Specific steps as follows:
1. Tungsten concentrate was treated with alkali and alkaline sodium tungstate obtained;
2. Add acidic substances into the alkaline solution and heat for neutralization to get neutral sodium;
3. Dilute sodium tungstate to get pre-exchange solution;
4. Use Weak-base anion-exchange resin to adsorb tungsten;
5. Use of desorbent for desorbing Weak-base anion-exchange resin with tungsten, and get desorption;
6. Removing impurities in the desorption;
7. Evaporate and crystallize the solution to obtain ammonium paratungstate.

Using ion exchange method based on Weak-base anion-exchange resin for preparing ammonium paratungstate, can shorten the process, complete the tasks of removing impurities and transformation at the same time. Besides it got high recovery rate of tungsten with sample equipment, and effectively improves the concentration of tungsten in the feed solution of ion exchange process. Also it cuts down the amount of wastewater, and prepare qualified APT products ultimately.

With the decreasing of high-quality tungsten ore, tungsten ore with high molybdenum has increasingly become an important raw material in metallurgy of tungsten, and it requires higher technology in separation of tungsten and molybdenum. A new ion exchange method based on three column series which is used to removing molybdenum in tungsten ore or fine mud to get pure ammonium paratungstate in low cost is presented in this paper. Three column ion exchange adsorption has a high capacity in adsorption and removing molybdenum effectively (the rate beyond 95%), reduce the number of resin regeneration and tungsten loss, also the consumption of auxiliary materials has been cut down.



Steps are as follows:
1. Ball grounding tungsten ore or fine slime, leaching with alkali, filtering, and concentrated to obtain sodium tungstate crystal;
2. Dissolve in and filter the sodium tungstate, then vulcanization;
Control WO₃ in sodium tungstate solution at 130-180g/L, pH value less than 12, adding Na₂S solution in accordance with S₂^- 1 ~ 8g/L, and then with adjust pH value to 7~10 by dilute H₂SO₄, heating to 60-80℃ and insulation for 0.5 to 5 hours;
3. Remove molybdenum by ion exchange;
4. Remove sulfur from sodium tungstate;
Inlet air into sodium tungstate under the condition of alkaline, and heating to make S₂^- to turn into sulfur or sulfide precipitation;
5. Remove impurities by method of ion exchange, then desorbs tungsten with ammonia and ammonium chloride solution to prepare ammonium tungstate;
6. Evaporate and crystallize to get APT.

Both direct current (DC) plasma spraying and radio frequency induction plasma spraying were conducted in the spraying chamber connected to a vacuum system. The soft vacuum/low pressure (10-30KPa) of the spray chamber was used for preventing the oxidation of tungsten particles melted in plasma. Ar was used as secondary plasma gas. The substrate used is a hollow copper cylinder with approximately 20mm in diameter and 400mm in length. The hollow cylinder was mounted on a rotary shaft cooled by high pressure cooling water. Fine tungsten powder used as spray feedstock has the mean particle size of 5μm and coarse tungsten powder has the particle size in the range from 45μm to 75μm.

During DC plasma spraying, tungsten coatings were generated by moving plasma horizontally on the rotary copper substrate. A sphere-shaped chamber with about 1500nm in diameter was used. Tungsten powder was laterally fed into the plasma via two opposite powder injectors. In addition, during radio frequency induction plasma spraying, tungsten coatings were generated by moving the copper substrate horizontally and rotating it simultaneously because plasma torch was fixed to an oscillating unit of power supply system and could not be moved. On the contrary, lateral injection of powders in DC plasma spraying, tungsten powders were axially fed into the center of the plasma with a water-cooled powder injector in induction plasma spraying. It should be pointed out that spray distance was calculated from the tip of water-cooled powder injector to the surface of the copper substrate. Tungsten coatings on the substrate were cooled to room temperature before being taken out from the spray chambers. Coating samples were cut by a low speed rotary diamond saw. After being ground and polished, the samples were examined under scanning electron microscope (SEM). Density of the coating, chiseled from the copper substrate, was measured using the method of water displacement.