Studies On Production Sodium Dichromate From Solid Wastes

Sodium dichromate is the intermediate product of the production process of chromium salt, which is widely used in various sectors of the national economy. The serious pollution caused by the chromite preparation of sodium dichromate-containing chromium series products has been constraining the sustainable development of the chromium salt industry. China is in the shortage of chrome ores, but the chromium slag pollution is more and more serious. Therefore, the preparation of sodium dichromate from chromium waste to realize clean production in chromium salt industry is significant task. We used Chromium-containing wastes from stainless steel smelting and processing industry as raw materials in our research, studied the process of sodium dichromate by roasting-sulfuric acid, cleared raw material chemical composition, particle size and the ratio of raw materials such as oxidizing roasting of charge stage, explored the necessary conditions for preparation of high purity sodium dichromate, prepared the sodium dichromate in the industrial process of implementation, and proposed a cost-effective and efficient way to use chromium residue.The main findings of the trial and progress are as follows:1) The chromium-containing residue particle size to60meshes is appropriate in the oxidation roasting process. The best conditions for the calcination process of chromium slag are as follows:the calcination temperature is1000℃, m (sodium carbonate):m (chromium slag)=0.18, the amount of oxide fillers is6g, the calcination time lasts8h.2)Soaking time and soaking solid ratio have a certain impact on chromium recovery in the sodium chromate clinker leaching process.When the leaching time is2h and the soaking solid ratio is1:1, chromium recovery rate will be up to99.3%.3) In the process of sodium chromate solution neutralization and cleaning, some parameters are as follows:the pH value is6.5, the neutraliaing solution concentration is120g·L-1, the neutralization reaction tempreture is60℃. the removal rate of impurity ions will be up to97.6%or more. 4) In the separation process of evaporation of the sodium dichromate solution and sodium sulfate, when the acidification of pH value is3.5, the feed concentration of Na2Cr2O7·2H20is1800g·L-1, the system saturation point temperature of Na2Cr2O7·2H2O-Na2SO4is128℃, Na2SO4will be separated basically.5) Influence on the purity of sodium dichromate is the main factor of the crystallization time and mass concentration. Crystallization time to12h is advisable. Mass concentration in74%is as well. The product of high purity will reach99.5%.6) Industrial preparation of sodium dichromate, a crystallization rate is up to48%, the purity is99.2%, and the quality reach the first-class quality standard in GB1611-92of "industrial sodium dichromate".7) Slag iron content46.6%, consistent with an iron ore of iron content, can be used for smelting. Sodium dichromate of175KG can be produced from one ton waste residue. Preparation1tons industrial sodium dichromate can produce economic benefits3570yuan.