The freezing crystallization method was adopted to recover sodium carbonate in the sodium tungstate liquid,achieving the reuse of sodium carbonate as the production raw material and reducing the discharge of salty wastewater.The effects of liquid concentration,freezing temperature,freezing time and seed crystal addition amount on the freezing crystallization process were studied.The results show that when the simulated leaching liquid containing 200g/L WO3and 200g/L Na2CO3is processed,Na2CO3crystallization rate reaches 75%and WO3loss rate is only 1.9%under the conditions of freezing time of 2h,freezing temperature of 4~5℃and seed crystal addition amount of 0.5%.Under the above conditions,the actual leaching liquid containing 200g/L WO3and 200g/L Na2CO3and obtained by Na2CO3pressure lea-ching of low-grade tungsten ore is processed,and Na2CO3crystallization rate is 74%and WO3loss rate is 6.6%.When Na2CO3recovered by freezing crystallization is returned to the pressure leaching process of tungsten ore,the obtained leaching residue contains 0.52%WO3,and the leaching rate is up to 94.99%,which can meet the requirements of industrial recycling production.

Tungsten can be efficiently leached from low grade scheelite by sodium phosphate-sodium hydroxide-calcium fluoride synergistic leaching,but the crude sodium tungstate leaching solution contains a certain amount of impurities of fluorine and phosphorus.Magnesium chloride was used as impurity removal agent to remove fluorine and phosphorus from the crude sodium tungstate solution in the form of precipitate.The effects of magnesium chloride dosage,temperature,pH value,initial fluorine concentration and reaction time on impurity removal were investigated.The experimental results show that increasing the amount of MgCl2,reaction temperature and reaction time is beneficial to improving the removal effect of fluorine and phosphorus,but too large or too small pH value is not conducive to the removal of impurities.When initial fluorine concentration is 1.35~2.85g/L and initial phosphorus concentration is 0.18g/L,the optimal process conditions are as follows:the molar ratio of magnesium to fluorine is nMg/nF=0.9,the temperature is 80℃,the pH value of solution is 11.8,and the reaction time is 30min.The removal rates of fluorine and phosphorus reach 98.3%and 97.2%,respectively,while the loss rate of tungsten in the precipitation slag is about 0.15%.Therefore,magnesium chloride precipitation method can effectively remove fluorine and phosphorus from sodium tungstate solution with low tungsten loss.

In order to solve the problem of low leaching rate and impurities of phosphorus and silicon in the leaching solution of industrial molybdenum oxide in atmospheric pressure ammonia-leaching process,the optimized conditions of ammonia-leaching of industrial molybdenum oxide at oxygen pressure were studied,and the feasibility of reducing phosphorus and silicon content in leaching solution by adding MgO and CaCO3was explored.The results show that the optimized conditions of oxygen-pressure ammonia-leaching of industrial molybdenum oxide are as follows:ammonia concentration 6.5%,liquid-solid ratio 3∶1,oxygen pressure 1.5MPa,leaching temperature 130℃,leaching time 3h,and stirring speed 350r/min.Under the optimized conditions,the molybdenum leaching effect is the best,and the leaching rate reaches 98.04%.In addition,MgO has better inhibition effect on phosphorus and silicon than CaCO3,and the lea-ching rates of phosphorus and silicon are 3.04%and 5.06%,respectively,having no effect on molybdenum leaching.The oxygen-pressure ammonia-leaching process of industrial molybdenum oxide has the advan-tages of simple operation,high molybdenum leaching rate,and obvious inhibition effect on phosphorus and silicon.The obtained ammonium molybdate solution is relatively pure,which is favorable for subsequent molybdenum production.

The feasibility was explored of selective reduction of niobium concentrate,and the effect was studied of temperature on the selective reduction of iron and niobium in carbon-matched pellets of niobium concentrate,as well as the occurrence states of iron-bearing phases and niobium-bearing phases in the reduction process.The results show that as the reduction temperature of niobium concentrate increases,the reduction metallization rate of iron minerals also increases.When the reaction temperature is 1050℃,the hematite in the niobium concentrate can be effectively reduced to metallic iron.However,there is still a certain amount of iron olivine in the reduction product,resulting in a reduction metallization rate of only 76.16%.CO content of the reducing atmosphere inside carbon-matched pellets of niobium concentrate is around 72.4%,which is significantly lower than 99%,the theoretical equilibrium value of carbon gasification.During the reduction process,niobium minerals remain in an oxygen-bearing state,which is beneficial to the subsequent separation of iron and niobium.The technological expectation of selective reduction of iron and niobium in niobium concentrate can be realized.

Using the filter residue after titanium extraction from titanium slag by concentrated sulfuric acid roasting method as the experimental material,the SiO2in the filter residue was leached with NaOH solution.The effects of stirring speed,liquid-solid ratio and alkali-residue mass ratio on the leaching rate of SiO2 were determined,and the kinetics of leaching reaction was explored.The results show that there is little effect of stirring speed on SiO2leaching rate,and with the increase of leaching temperature and time,liquidsolid ratio and alkali-residue mass ratio,the leaching rate of SiO2increases.The leaching process is controlled by chemical reaction,the apparent activation energy is 42.89kJ/mol,and the kinetics equation can be expressed as 1-(1-x)1/3=0.44×103×[-42887/(RT)]×t.

The manganese dioxide was used to oxidize and leach vanadium from raw material of the stone coal vanadium ore from Zhangjiajie.The effects of MnO2dosage,liquid-solid ratio,leaching time,H2SO4 dosage and leaching temperature on vanadium leaching rate were investigated.The results show that the leaching rate of vanadium reaches 94.17%under the conditions as follows:MnO2dosage of 3%,liquid-solid ratio of 0.8∶1,H2SO4dosage of 35%,leaching temperature of 95℃and leaching time of 10h.The vanadium leaching rate Rhas a good linear relationship with the leaching time t in the form of 1-(1-R)1/3.The apparent activation energy of the leaching reaction is approximately 54.62kJ/mol according to the Arrhenius equation,indicating that the reaction is controlled by a chemical reaction.

Zirconium is an indispensable structural material of nuclear reactors for its very low thermal neutron absorption cross section,which will not absorb and waste thermal neutrons during the nuclear reaction process.The production process of zirconium metal is mainly introduced.The advantages and disadvantages of such zirconium metal production methods as metal thermal reduction,molten salt electrolysis and thermal dissociation of zirconium iodide are compared and analyzed,and the development trend of zirconium metal production process is put forward.

The process was studied for oxidizing divalent iron to trivalent iron in sulfuric acid reduction leaching solution of heterogenite from Congo(Kinshasa)by sodium sulfite and air co-oxidation.The effects were also analyzed of acidity,sodium sulfite addition amount and air flow on oxidation efficiency.The results show that divalent iron in 2500mL leaching solution can be completely oxidized for 5hunder the conditions of solution pH of 3.8,air flow of 150~200L/h,reaction temperature of(40±5)℃and sodium sulfite addition amount of 5g.

Spherical yellow tungsten prepared by spray technology with AMT as raw material has the characteristics of small particles,hollow inner structure,high activity and easy reduction.Nano-sized tungsten powder can be prepared by hydrogen reduction of yellow tungsten,and then carbonized in hydrogen to form ultra-fine tungsten carbide powder with saturated carbon content.The phase and morphology of the powder were analyzed by XRD and SEM.The results show that the BET particle size of WC is only 0.163μm,and the particle size distribution is uniform without coarse particles.The quality of WC is up to the standard of high quality ultrafine powder.The cemented carbide samples prepared with the above WC as raw material have fine and uniform grains and good physical and mechanical properties,which can meet the needs of preparing high-performance cutting tools and drilling tools.

Using laboratory-made ultrasonic and microwave ball milling equipment,molybdenum disulfide(MoS2)was modified by the surface modifiers of oleic acid and stearic acid,and the modified molybdenum disulfide(MMD)was obtained.MMD was introduced into the base oil to test its dispersibility and tribological properties,and then the elements of the friction surface was analyzed.The results show that compared with the simple ultrasound method commonly used at present,the molybdenum disulfide modified by ultrasonic and microwave ball milling has more stable dispersion in the base oil.Besides,in the friction process,MMD is more likely to deposit on the friction surface,and tribochemically react with the friction surface to form a more complete lubrication film,thus achieving more excellent anti-friction and anti-wear performance.