The Stone Coal Vanadium New Technology And Its Mechanism

A novel process of extracting vanadium from stone coal is developed in this paper. It includes roasting—pressure alkali leaching—silicon removal—solvent extraction—precipitation—calcination, which is regarded as a clean, highly efficient and low cost process. By treating the refractory stone coal from a domestic plant, the recovery of vanadium reached 82.14% with the purity of final product V2O5 of 98.5%. The results demostrated the low reagent consumption, little waste discharge, high vanadium recovery of the process.There are some serious problems of the existing process of roasting—alkaline leaching to recover vanadium from stone coal, such as large alkali consumption, long leaching time and high impurity content in leach solution. To solve these problems, this paper proposes the pressure alkali leaching and investigates the effects of sodium hydroxide amount, liquid-solid ratio, leaching time, anion species and concentration on the leaching of vanadium from stone coal. The results showed that the leaching of vanadium reached 86% with sodium hydroxide addtion of 3.5% of ore weight and L/S ratio of 1.5 at 180℃for 2 h. The mass ratio of Si/V was 0.65 in the leach solution and the pH was 11.4. High pressure alkaline leaching process with the advantage of high leaching of vanadium but low leaching of other impurities provides a new way for extracting V2O5 from stone coal.Based on the properties of silicon, the pH of leach solution was firstly adjusted to 9.0-8.5 to precipitate most of silicon as solid H4SiO4. The rest of silicon existed as colloidal H4SiO4 was then removed using coagulation precipitation. The specified technique parameters are as follows:the pH of leach solution was firstly adjusted to 9.0-8.5 using H2SO4 solution before the temperature was raised to 90-95℃for 2 mins. The reagent of A12(SO4)3·18H2O of 0.1% solution weight was then added to the leach solution at 50℃for 30 mins. After filtration, The removal of silicon reached 97.48% while the recovery of vanadium 98.16%, indicating the very good separation of silicon from vanadium. According to the solution chemistry of vanadium and silicon in alkaline solution, the organic system of 15% N263+10% TBP+75% sulfonated kerosene was determined to extract vanadium from silicon. With 3-stage counter current extraction, the concentrations of V2O5 in raffinate was less than 0.01g/L while the concentrations of V2O5 and SiO2 in organic solution was 24 g/L and 0.1 g/L, respectively. The raffinate was recycled to leaching step after the supply of sodium hydroxide. The cumulative concentrations of SO42-and Cl- in leach solution were less than 10 g/L and 7g/L, respectively. The loaded organic solution was washed using pure water for one time before being stripped. The mechanism of extraction can be expressed as follow:3(R4N)Cl+V3O93-= (R4N)3V3O9+3Cl-Stripping of loaded organic solution was excellent using 0.7 mol/L NaOH and 2.5 mol/L NaCl mixed solution with three stage counter-current and O/A of 5:1 at ambient temperature for 2 mins. More than 99% of V was stripped and the concentration of V2O5 in the strip liqor reached of 126 g/L with pH value of 10.2. The stripping reaction can be expressed as follows:2(R4N)3V3O9+6OH-+6Cl-= 6R4NCl+3V2O74-+H2O(R4N)3V3O9+3Cl-=6R4NCl+V3O93-The vanadium in strip liquor was precipitated using NH4C1. After pH adjust of the strip liquor from 10.2 to 9.0, the precipitation of vanadium reached 99.7% with the solid NH4C1 addition of KNH4Cl=1.47 at 45℃for 1 h stirring followed by at ambient temperature for 4 h. After drying and calcining,, the purity of final product V2O5 reached 98.5%, meeting the standard specification.The advantages of this process are as follows:Low reagent consumption and waste emission since "water", "salt" and "organic phase" can be recycled; Easy operation of pressure alkali leaching since the equipment anticorrosion can be easily solved. Simple process with high vanadium recovery. In a word, application of this process in industry is expected to make an important impact on the extraction of vanadium from the stone coal and to deliver good economical benefits.