Research On New Technology Of Chromium Removal By Wet Phosphoric Acid Extraction

There are many purification processes for wet-process phosphoric acid,mainly chemical precipitation,adsorption,electrodialysis,ion exchange and solvent extraction.The company requires whether the chromium-phosphorus ratio meets the requirements(Cr:mg/L,P:the percentage of P₂O₅ in the solution)to reflect the quality of the experimental results.The chromium content in the raw materials in this paper is 63.3ppm,phosphorus content 288.1g/L,and the chromium-phosphorus ratio is 1.17.In the current research field,the commonly used method is to use ion exchange method for treatment.The removal rate of chromium can reach about 88%.However,this method uses a large amount of resin and is difficult to regenerate,so this article aims at the problem of phosphoric acid dechromization,and uses extraction to purify phosphoric acid.This paper studies the extraction performance and optimal extraction conditions of different extractants,and compares the extraction results between the multi-channel microreactor made by 3D printing and the conventional device.Conventional extraction studies the effects of phase ratio,different extraction systems,extractant volume fractions,and temperature on the experimental results under conventional single-stage extraction conditions.When the temperature is room temperature,the shaking time is 20 minutes,and the phase separation time is 15 minutes,the main results obtained are conclusion as below:(1)In the isoamyl alcohol system,when the optimized process parameters are obtained,the single-stage extraction rate reaches the highest when the phase ratio is 1:5,the extraction rate of phosphoric acid is as high as 74.37%,the back extraction rate of phosphoric acid is 46.55%,and the ratio of chromium to phosphorus is 0.23;With the increase in the volume fraction of the extractant,from 30%to 100%,the extraction rate of phosphoric acid rose from 37.75%to 73.04%,the back extraction rate of phosphoric acid dropped from 77.24%to 48.4%,and the ratio of chromium to phosphorus rose from0.22 to 0.24.(2)In the TBP system,when the optimized process parameters are obtained,the single-stage extraction rate reaches the highest when the ratio is 1:5,the extraction rate of phosphoric acid is as high as 60.38%,the back extraction rate of phosphoric acid is98.51%,and the ratio of chromium to phosphorus is 0.12.A microfluidic extraction experiment of phosphoric acid was carried out.In the experiment,two different microreactors were used for the experiment,and the experiment only performed single-stage extraction.The main conclusions drawn are as follows:(1)When using a microreactor with a length of 78.25mm,a width of 32mm,a height of 18mm,a microchannel inner diameter of 1mm,and a liquid holding capacity of4.5m L for the extraction experiment.when the phase ratio is 1:3,the flow rate is 50:100(m L/min),and the residence time is 1.68s.The extraction rate of phosphoric acid reaches the maximum value,the highest is 31.00%,the stripping rate is 38.43%,and the chromium-phosphorus ratio is 0.09.(2)When using a microreactor with a length of 139mm,a width of 38mm,a height of 18mm,a microchannel inner diameter of 1mm,and a liquid holding capacity of4.9m L for the extraction experiment.when the phase ratio is 1:1.84,the flow rate is40:80(m L/min),and the residence time is 2.5s.The extraction rate of phosphoric acid reaches the maximum value,the highest is 40.00%,the stripping rate is50.47%,and the chromium-phosphorus ratio is 0.09.