A direct hydrometallurgical route for nickel and molybdenum extraction from a nickel-molybdenum （Ni-Mo） ore using pressure acid leaching was studied. The nickel and molybdenum were extracted by acid leaching under oxygen pressure. Compared with traditional roasting methods, this hydrometallurgical method eliminates SO2 and As203 emission （the Ni-Mo ore containing 15%-25% S）. Compared with existing alkali leaching recovery of molybdenum process, almost all the nickel and considerable molybdenum were extracted in the acid leaching process. Under oxygen pressure conditions, almost all the nickel and a substantial part of the molybdenum were dissolved into the acid leaching liquor and the other part of the molybdenum was left in the acid leach residue. The acid leach residue was further leached under alkaline （NaOH） conditions. Under optimal experimental conditions, the extraction rates nickel and molybdenum reached 97% and 96%, respectively.
Vanadium extraction from stone-coal was investigated by oxygen pressure acid leaching and solvent extraction.The mineralogy of the stone-coal from Tongren City of Guizhou Province,China,was investigated by various determination methods. The effects of leaching time,leaching temperature,leaching agent concentration,leaching L/S ratio,granularity of material,additive consumption were investigated based on the mineralogy.The results show that under the conditions of leaching time of 3-4 h, temperature of 150℃,sulfuric acid consumption of 25%?30%,ratio of liquid to solid of 1.2:1,the granularity less than 0.074 mm, additive consumption of 3%-5%,and oxygen pressure of 1.2 MPa,and the vanadium leaching rate can be more than 92%by the method of two-step pressurized acid leaching.The powdery V2O5 product with 99.52%in V2O5 content is obtained by the flowsheet of acid recovery,removing iron by reduction process,solvent extraction,precipitating vanadium with ammonium water,and pyrolysis from the stone-coal oxygen pressure acid-leaching solution.The total recovery efficiency of vanadium is above 85%,which is more than 20%higher than that obtained in the conventional process.Furthermore,the new process does not cause air pollution since no HCl or Cl2 is released by calcination of the raw material.
The recovery of vanadium from a black shale from Guizhou Province of China was performed using a three-step process, which consists of a leaching step in the H2SO4-HF-NaClO system under atmospheric pressure,the vanadium separation from leachate by solvent extraction and stripping,followed by precipitation of ammonium vanadate and thermal decomposition.Under the optimum leaching conditions of 100 g/L sulfuric,15 g/L hydrofluoric acid,1.5 g/L NaClO,6 h leaching at 90℃and oxygen partial pressure of 1 200 kPa,and the liquid-to-solid ratio of 2,about 91%vanadium extraction is achieved.The vanadium extraction yields of solvent and stripping are 99.83%and 97.66%when using 10%(volume fraction)P204,5%TBP and 85%sulfonated berosene as organic phase and 15%(mass fraction)sulphuric acid as stripping agent.After thermal decomposition the purity of powder vanadium pentoxide products is 99.18%and the overall vanadium recovery is over 81%in the whole process.
The dissolution kinetics of vanadium trioxide in sulphuric acid-oxygen medium was examined. It was determined that the concentration of sulphuric acid and stirring speed above 800 r min 1 did not significantly affect vanadium extraction. The dissolution rate increased with increasing temperature and oxygen partial pressure, but decreased with increasing particle size. The dissolution kinetics was controlled by the chemical reaction at the surface with the estimated activation energy of 43.46 kJ·mol-1. The leaching mechanism was confirmed by characterizing vanadium trioxide and the dissolution residue using SEM-EDS analysis. Combined with thermodynamic calculation, the pressure leaching of vanadium trioxide in the temperature range (100 to 140 ℃) studied occurs as follows: V2O3 + O2 + H2SO4 = (VO2)2SO4 + H2O.
