Study On The Technology Of Sodium Hydroxide Leaching-Direct Solvent Extraction Of Tungsten From Shizhuyuan Complex Low Grade Tungsten Ore

Abstract:Pure compound Ammonium Paratungstate from alkaline-leach liquor of tungsten ores is very important during tungsten hydrometallurgy. A novel process to treat complex middle grade scheelite-wolframite mixed ore from Shizhuyuan (Hunan province) with environmental friendliness and low cost was developed in the paper, including sodium hydroxide-sodium phosphate pressure leaching of tungsten ore, direct solvent extraction of tungsten from the leach solution and recycling leaching of the ore with the raffinate. This process exhibits advantages of simple flow sheet and no wastewater discharge, which can be easily industrialized.The research and results are mainly concluded as follows:(1) High pressure leaching of tungsten oreSodium hydroxide-sodium phosphate pressure digestion was selected through comparing the effect of different leaching agent. And the optimization experiment showed that the leaching rate of WO3, As, SiO2and Mo was98.49%,62.40%,3.14%,93.31%respectively, and the mean rate of WO3in the residue was1.561%, when the addition of NaOH is1.5times theoretical amount, Na3PO4is1.0times theoretical amount, liquid-solid ratio is3:1, temperature is160℃and time is3h. Except Molybdenum, the primary separation of WO3and main impurities was achieved, which alleviated the burden of impurity removal in subsequent step.The behavior of P, As and SiO2was studied in order to restrain from leaching of these impurities. And the effect of adding MgO was investigated in the leaching process.(2) Direct solvent extraction of tungsten from alkaline-leach liquorThe mechanism of extraction of tungsten by carbonate quaternary ammonium salt proved by saturated capacity method can be expressed below: WO42-(aq)+(R4N)2CO3(org)=(R4N)2WO4(org)+CO32-(aq) The saturated concentration of WO3in organic phase was90.2g·L-1, when the concentration of WO3in feed liquid was112.23g·L-1, temperature25℃, phase ratio1.5:1, duration of oscillation5min and the organic solution consisted of50%TOMAC(400g/L)+20%ec-caprylic30%kerosene. After7stages of counter-current extraction, the extraction rate of tungsten reached99.7%, leaving less than0.3g·L-1WO3in the rafffinate. The behavior of Mo followed WO3, the extraction rate of Mo was up to99.5%and a small amount of P, As, Si was extracted into organic phase, resulting in removal rate of P, As, and Si was96.85%,93.36%,66.17%, respectively.The stripping isotherm was plotted by the method of phase ratio variation. The concentration of WO3could up to119.37g/L, when the concentration of WO3in the loaded organic was73.44g/L, temperature20℃, phase ratio15:1, duration of oscillation5min, single stage stripping and the stripping agent consisted of3mol/L+1mol/LNH3·H2O,. After12stages of counter-current extraction when the flow ratio2:1and phase ratio1:1, the concentration of WO3in strip liquor was above124g/L and the WO3in the unloaded organic below4g/L. Meanwhile, the concentration ratio of P/WO3, As/WO3, Si/WO3was0.000646,0.000326and0.000541respectively, which meet the requirements of producing APT-0.(3) Recycling leaching with rafffinateTo achieve closed circle of water in direct extraction of tungsten from alkaline solution, reusing raffinate as leaching agent is important. The research showed that directly leaching with untreated raffinate would cause the accumulation of all kinds of impurity ions to varying degrees, but had no impact on the effect of decomposing the tungsten ores.The inhibitor A which used to purify the raffinate before leaching was chosen. Beside Mo and SO42-, the concentration of As, Si, Cl-, F-etc. in the leaching agent could decrease through reusing the purified raffinate, however the leaching rate of WO3was reduced simultaneously. To refrain from lowering WO3leaching rate, more sodium phosphate was added.As a clean metallurgical technology, the process of sodium hydroxide-sodium phosphate pressure leaching of tungsten ore followed by direct solvent extraction of tungsten from the leach solution exhibited advantages of simple process, high recovery of tungsten, less corrosion of equipment in the whole alkaline system, low consumption of reagent and no wastewater discharge.