Recycling And Recovery Of Metal Ions From Spent Steel Pickling Wastewater

Stainless steel pickling wastewater usually contains high concentration of nitric acid,hydrofluoric acid,and metal ions such as iron,chromium,and nickel,which has the characteristics of high toxicity,high acidity,and difficult handling.The traditional method of neutralization precipitation has several defects such as high cost and secondary pollution.Meanwhile,valuable acid and metal resources can not be recovered.Acid recycling and efficient separation of metal ions are still difficult in recently modified neutralizing precipitation processes.In this thesis,a large amount of metal salt crystals were produced after recycling nitric acid and hydrofluoric acid from stainless steel pickling wastewater with the method of vacuum evaporation.The economic and feasible process route was developed to recover the metal ions from pickling wastewater.There we gave the following conclusions:?1?In order to strengthen the extraction process,a synergistic extraction system for removing iron from the high-acidity sulphates solution was developed.N235-P204synergistic system was suitable for iron removal due to its high extraction efficiency,fast extraction kinetics,and easy iron stripping.The effects of various parameters on the extraction of iron were investigated.The optimum extraction conditions:the extraction composition was N235:P204:sulfonated kerosene=3:3:4,with the pH value 1.5,the O/A ratio 1:1 for 5 min at room temperature.After two stages of extraction,the extraction rate of iron reached 99.05%,and the loss rates of chromium and nickel were 3.30%and2.36%,respectively.The effects of various parameters on the stripping of iron were investigated.The optimal stripping conditions:the stripping agent was 0.1 mol/L ammonia,with the O/A ratio 1:2 for 3 min at room temperature,and the primary stripping rate of iron reached 91.21%.The stripping solution was precipitated by ammonia,and the precipitate was calcined to obtain a high-purity iron oxide product.The recovery rate of iron was 99.05%,the purity of chromium hydroxide product was98.73%and the yield was 48.83 kg/m³ wastewater.Chromium and nickel were recycled by neutralization precipitation method,the recovery rate of chromium was 96.70%,the purity of chromium hydroxide product was 95.52%and the yield was 13.98 kg/m³wastewater.The recovery rate of nickel was 97.64%,the purity of nickel carbonate product was 98.29%and the yield was 8.33 kg/m³ wastewater.?2?Extraction kinetics and extraction mechanism of new synergistic extraction system had been studied.The plot of log D_Fe vs.log[H⁺],log[SO₄^2-],log N235 and log P204 was straight lines with slope values of-0.9608,1.1313,1.3165 and 1.8212,respectively indicating the association of one OH^-,one SO₄^2-,one N235 and two P204ions with the extracted species.We were studied to show the extraction of monomeric and dimeric forms of the hydrolyzed complex,Fe?OH?SO₄.The extraction reaction equation was:Fe³⁺_Aq.+H₂O+SO^2-_4Aq.+R₃N_Org.+2?HA?_2Org.?Fe?OH??SO₄?·R₃N·2?HA?_2Org.+H⁺_Aq.?3?Iron was recycled by jarosite method at 90?for 120 min,and the removal rate of iron was above 80%.Chromium and nickel were recycled by neutralization precipitation method,and the recovery rate of chromium was 90.39%,while the purity was 48.84%and the yield was 25.55 kg/m³ wastewater.The recovery rate of nickel was74.19%,while the purity was above 98%and the yield was 6.33 kg/m³ wastewater.?4?The extraction method was used to remove iron from the solution after jarosite reaction.The optimum extraction conditions:the extraction composition was 5%N235-5%P204-90%sulfonated kerosene,with the pH value 1.5,the O/A ratio 1:1 for 5min at room temperature,and the primary extraction rate of iron was 92.82%.Chromium and nickel were recycled by neutralization precipitation method,the recovery rate of chromium was 89.14%,the purity of chromium hydroxide product was92.92%and the yield was 13.24 kg/m³ wastewater.The recovery rate of nickel was92.71%,the purity of the nickel carbonate product was above 98%and the yield was7.91 kg/m³ wastewater.According to the above method,the iron was removed by jarosite and extraction method,chromium and nickel were recycled with neutralization precipitation method.This technology was relatively economic and feasible,the loss rate of chromium and nickel was small,and the purity of chromium and nickel products were higher.This technology realized separation and recovery of iron,chromium and nickel.