Study On The Theory And Technology Of Acid Treatment Of Neutralized Residue In Straw Sedimentation Solution

Oxalic acid precipitation is an important way to produce rare earth oxides with high purity,good performance and good morphology.The neutralized residue of straw precipitated liquid is the waste residue produced by lime neutralizing straw precipitated liquid.At present,most of the neutralized residues after straw sedimentation are disposed of by stacking and landfill,which will not only occupy the land,but also pollute the environment.At the same time,oxalic acid can not be recycled,resulting in a waste of resources.Therefore,the high-value utilization of neutralization residue of rare earth grass after sedimentation provides a research idea for promoting the sustainable development of secondary resources.Therefore,this paper takes the neutralized residue of grass precipitated liquid produced by a rare earth smelter in southern Jiangxi as the raw material,investigates the leaching behavior of neutralized residue in different acid systems and the crystallization behavior of oxalic acid in simulated solution through systematic experiments,and obtains the favorable conditions for efficient leaching and crystallization separation of oxalic acid in neutralized residue.The main research contents and conclusions of this paper are as follows:(1)By drawing the lgc-p H diagram of calcium oxalate dissolution equilibrium and the relationship diagram of calcium oxalate dissolution equilibrium in hydrochloric acid and sulfuric acid system.According to thermodynamic calculation and analysis,calcium oxalate is dissolved in hydrochloric acid system.If oxalic acid and calcium chloride exist in the initial solution,the dissolution of calcium and oxalic acid in calcium oxalate will be significantly inhibited;In the presence of sulfate,increasing the concentration of sulfuric acid will change calcium oxalate into calcium sulfate,which will promote the reaction;When sulfuric acid dissolves calcium oxalate,when the initial solution contains oxalic acid,the inhibitory effect of the initial oxalic acid concentration on the decomposition of calcium oxalate by sulfuric acid is significantly weaker than that by hydrochloric acid decomposition system.By comparing and analyzing the experimental data with the thermodynamic calculation data,we can know that the change trend of the actual data and the theoretical data is basically the same,which reflects that the thermodynamic calculation has guiding significance for the experiment.(2)Based on the study on the leaching behavior of neutralized residue after straw precipitation in sulfuric acid system,the best leaching conditions were selected.The results show that the optimum conditions for leaching oxalic acid in sulfuric acid system are reaction temperature 95℃,sulfuric acid concentration 4 mol/L,reaction time 4 h and liquid-solid ratio 5:1.The main component of neutralization slag is calcium oxalate,which is transformed into calcium sulfate precipitation in sulfuric acid system,so the calcium concentration has been at a low level.The neutralization Residue Leached by sulfuric acid system can effectively separate oxalic acid and calcium.(3)Based on the leaching behavior of neutralized residue in straw precipitation solution in hydrochloric acid system,the optimal leaching conditions were selected.The results show that the optimum conditions for leaching oxalic acid and calcium in hydrochloric acid system are reaction temperature 80℃,hydrochloric acid concentration12 mol/L,reaction time 2 h and liquid-solid ratio 7.5:1.The calcium leached by hydrochloric acid system exists in free state,and 1:1 sulfuric acid is added for calcium precipitation.The experimental results show that the optimal conditions for calcium precipitation are precipitation temperature 20℃ and S/Ca 3.0.By phase analysis,the precipitated calcium product is calcium sulfate,and the precipitated crystal morphology produced at high temperature is better.(4)The crystallization of oxalic acid in simulated hydrochloric acid and sulfuric acid system was investigated.The results show that low temperature conditions are conducive to the crystallization of oxalic acid and are relatively stable.In hydrochloric acid system,the optimum crystallization conditions are crystallization temperature 0℃ and hydrochloric acid concentration 2 mol/L;In sulfuric acid system,the optimal crystallization conditions are crystallization temperature 0℃ and sulfuric acid concentration 1 mol/L.Recrystallization can effectively remove sulfur and chlorine from oxalic acid solution.