Study Of Alkali Melting Decomposition-Water Leaching Process Of Scrap Carbide Inserts And Removal Of Chromium And Vanadium

Cemented carbide,as the most important application area for tungsten consumption,inevitably generates a large amount of waste cemented carbide,of which the tungsten content is up to 74%～91%and the cobalt content is 3%～16%.Achieving efficient recycling of scrap cemented carbide can not only alleviate the demand for strategic metals such as tungsten and cobalt in China,but also reduce the pollution level of the environment and meet the requirements of developing circular economy.In response to the problems of long process flow,unsatisfactory tungsten-cobalt separation effect,high cost and poor process applicability of traditional recycling and treatment technology for waste carbide,this paper adopts the process of"alkali melting decomposition-water leaching"to treat lump waste carbide,which can achieve alkali melting decomposition of lump carbide in one step without pretreatment such as oxidation decomposition,physical crushing and ball milling,and obtain crude sodium tungstate by At the same time,the Cr and V content in the crude tungstate solution is easily exceeded,which affects the subsequent product quality,and the chromium and vanadium removal by ferrous salt precipitation is investigated.The main research contents and conclusions of the paper are as follows:（1）Thermodynamic calculations of the chemical reactions that may occur during the alkali melting decomposition of scrap cemented carbide were carried out andΔ_TG^θ-T diagrams were drawn.The results show that WC is able to react with Na OH,Na₂CO₃ and Na HCO₃ to produce Na₂WO₄;Co does not participate in the alkali reaction and is oxidized to Co O or Co₃O₄;Cr₃C₂reacts at different alkali melting decomposition temperatures to produce Na₂Cr O₄ or Na₂Cr₂O₇,and VC is produced as Na VO₃,Na₃VO₄ or Na₄V₂O₇.（2）The experimental study of alkali decomposition-water immersion process was carried out,and the decomposition of the scrap carbide and the phase transformation of tungsten and cobalt were investigated by combining XRD,SEM and other analytical means.The experimental results showed that the effect of using Na OH as the alkali fusion additive was better;the higher the decomposition temperature,the more significant the signs of alkali fusion infiltration and the better the alkali transformation effect of WC;the better process conditions obtained were as follows:alkali melting decomposition temperature 900℃,the mass ratio of sodium hydroxide/scrap cemented carbide 1.7:1,alkali melting decomposition time 50min,leaching temperature 20℃,leaching time 60min,liquid-solid ratio 6:1 and The speed was 300r/min;under these conditions the alkali fusion decomposition rate of lumped scrap tungsten carbide reached 100%,and the tungsten leaching rate was as high as 99.56%,and the filtrate was Co O.（3）To investigate the thermodynamic analysis of Cr and V removal by precipitation of iron or ferrous salts from crude sodium tungstate solution,Eh-p H diagrams of Cr-Fe-H₂O and V-Fe-H₂O systems were plotted,and thermodynamic equilibria of Cr⁶⁺-Fe³⁺-V⁵⁺-H₂O and Cr³⁺-Fe²⁺-Fe³⁺-V⁵⁺-H₂O systems were constructed.It was shown that the Cr⁶⁺-Fe³⁺-V⁵⁺-H₂O system was not feasible to remove chromium and vanadium from crude sodium tungstate solution by iron salt precipitation;however,the analysis of the Cr³⁺-Fe²⁺-Fe³⁺-V⁵⁺-H₂O system showed that the simultaneous removal of chromium and vanadium from crude sodium tungstate solution by subiron salt precipitation was feasible,and Cr（VI）was reduced by Fe²⁺or Fe（OH）₂ in the alkaline system Cr（VI）was reduced by Fe²⁺or Fe（OH）₂ in alkaline system and hydrolyzed to form Cr（OH）₃ precipitate,while V（V）reacted with Fe²⁺or Fe（OH）₂ to form Fe（VO₃）₂ precipitate.By controlling the p H value within 7.6～9.3,the concentration of chromium,vanadium,iron and total ferrous ions in the solution could be reduced to less than 0.08g/L.（4）An experimental study of chromium and vanadium removal by ferrous salt precipitation from crude sodium tungstate solution was carried out.The results showed that when the solution p H was 9,the reaction time was 60 min,and ferrous sulfate was added at n(Fe²⁺):n（V+Cr）=15:1 at room temperature,the chromium removal rate was 99.84%,the vanadium removal rate was 95.05%,and the tungsten loss rate was 0.332%,and the experimental results were consistent with the thermodynamic calculations.This further confirmed the technical feasibility of simultaneous chromium and vanadium removal by ferrous salt precipitation.