Process Research And Production Improvement Of Preparation Of Chromium Oxide Green By Sodium Chromate Carbonization Mother Liquor

As a pigment product of chromium trioxide,chrome oxide green has advantages of high temperature resistance,corrosion resistance and excellent color rendition,which make it an irreplaceable ingredient in the production of inorganic pigments,ceramics and high-end abrasives.At present,domestic chromic anhydride calcination is mainly used to prepare chrome oxide green.However,there are some problems in this process,such as serious pollution of"three wastes",expensive raw materials and single product type.As a result,the high-end market of chromium oxide green is monopolized by foreign enterprises..At the same time,with the increasing attention of the state to environmental protection,the traditional production technology has been unable to meet today's demand for cleaner production,and elimination has become a time problem.In order to solve these problems,this paper takes the different carbonation degree mother liquor of sodium chromate carbonation with as the raw material to produce chromium hydroxide by hydrothermal method,The effects of process parameters and washing methods on sodium salt content in chromium hydroxide filter cake were investigated.Chrome oxide green was prepared by calcining chromium hydroxide under fixed calcining condition,and the technological parameters were determined The research results are as follows:?1?As the carbonization degree of the mother liquor increases,the required temperature is lowered from 240?to 180?when the Cr?VI?in the mother liquor reaches maximum reduction.Under fixed calcination conditions,chromium oxide green filter cake washed three times is beneficial to the preparation of chromium oxide green with uniform particle size.?2?The median diameter D?50?of chromic oxide green products increased from 1.12?m to4.22?m with the increase of carbonation degree.When the carbonation degree of raw materials was about 40%,the particle size distribution of Cr₂O₃ prepared was typical normal distribution,in which the diameter D?50?was 3.13?m.?3?Process parameters:The mother liquor carbonization degree is 40%,Cr?VI?content in the mother liquor is 350g/L?indicated by sodium bichromate?,the reaction temperature is240°C,starch excess coefficient is 1.4,washing water and the filter cake quality ratio of 2:1,the number of washing-ups is 3,the calcination temperature is 1000°C,calcination time 3 h.According to the raw materials,process operation conditions,economy and safety factors required in the process of chrome oxide green synthesis,based on the optimal process parameters,the preliminary industrial design of the 1000-ton chrome oxide green project was carried out.It includes material balance calculation,energy balance calculation,design calculation and selection of important equipment,as well as safety operation specifications and three waste treatment schemes.