Research On The Recovery Of Sulfuric Acid And Chromium(?) From The Waste Acid Of Stainless Steel Pickling Regeneration

China is the largest producer of stainless steel in the world.In the production process of stainless steel,a large amount of waste sulfuric acid containing various valuable metals will be produced.This paper proposes a process route of recovering sulfuric acid by solvent extraction or diffusion dialysis first and then effective recovering Cr(?)by hydrolysis method under low acidity in order to solve the problems of high concentration of regenerated sulfuric acid,high concentration of metal ions and complex composition in stainless steel pickling waste liquid,implements efficient recovery and clean reuse of waste acid and Cr(?)resources,and reduced the waste production amount and lower cost,has important theory value and practical significance.The conclusions of this study are as follows:(1)Recovery of free acid from waste acid by solvent extraction method.According to the study,the extraction system consisting of “40% TEHA+50% isomeric tridecanol +10% Exxsol D110” was extracted at 30? at O/A=2:1,and the extraction rate of sulfuric acid was up to 79.8%.In the condition of 30? and O/A=1:1,the reverse extraction rate of sulfuric acid reached 85.5% after three(theoretical)stages of reverse extraction,and the product acid could be returned to the pickling production line.(2)The diffusion dialysis method is used to recover the free acid in the waste acid.The research shows that when DF120 type anion exchange membrane is used to recover sulfuric acid,the recovery rate of sulfuric acid can reach 73% under the condition of waterto-material flow ratio of 1:1 and waste acid feed flow rate of 8.5 m L/min,and the product acid concentration is high,which can return to the pickling line.(3)The recovery process of Cr(?)in waste acid was determined.Studies have shown that the recovery of Cr(?)by high-temperature hydrolysis method,under the conditions of initial acid concentration 30 g/L,temperature 230? and time 24 h,the hydrolysis rate of Cr(?)can reach 81.8%,and the waste acidity rise after hydrolysis.At the same time,the effects of different neutralization precipitation methods for recovering chromium are compared.The experiment found that the neutralization method treats the regeneration of simulated waste acid,the alkali consumption is high and the sludge production is large,and the later disposal is difficult.(4)A complete process route for high efficiency recycling of pickling waste liquid and chromium recovery has been established,and the total acid recovery rate has been increased from 90% to 95% of the original process,and high efficiency recovery of chromium has been achieved.At the same time,the simple neutralization precipitation treatment process is compared,and it is found that the new process has obvious advantages such as high recovery rate of sulfuric acid and Cr(?),small waste generation and low cost.The "two-step method" for the treatment of stainless steel pickling waste acid regeneration,while achieving efficient recovery and reuse of sulfuric acid and Cr(?),greatly reducing waste emissions and effectively reducing industrial operating costs,has important theoretical value and practical significance.