Study On Reuse And Treatment Process Of Waste Metal Pickling Liquid

As a kind of cleaning agent, acid is widely used in metallurgy, machinery and metal products processing industry. When the acid concentration reduces to a certain extent, the cleaning effect is significantly decreased and become waste pickling liquid. Waste pickling liquid is acidic and contains large amounts of metal ions, so it is classified as hazardous waste. If not properly treated, it can cause serious environmental pollution and waste of resource. The traditional neutralization method will produce sludge as secondary pollutant, but also can not reach the purpose of recycling. In this work, the method for recycling of waste hydrochloric acid pickling liquid was studied, with a view to find a possible combination treatment for the recycling of waste pickling liquid and to provide guidance for its engineering application.The recycling of waste hydrochloric acid pickling liquid was carried out by vacuum evaporation. The optimum operation parameters were determined by orthogonal experiments. While application experiments of the prepared FeCl2crystals were carried out using bamboo wastewater to determine the optimum conditions for removal of chroma and turbidity such as dosage, pH, temperature and so on. Optimum process conditions for preparing PFAC using waste hydrochloric acid pickling liquid were studied. The self-prepared PFAC was used in bamboo wastewater flocculation treatment to explore the effect of PFAC dosage, pH, temperature and hydraulic mixing conditions on flocculation. Flocculation effect of self-prepared PFAC and commercially available products was compared. The pilot combination treatment and equipments for waste hydrochloric acid pickling liquid were designed and the economic possibilities were analyzed.Vacuum evaporation experiments showed that the optimum conditions were the dosage of concentrated sulfuric acid of6%, vacuum degree of0.06MPa, evaporation time of40min. The regenerate acid can be directly reused in the pickling process. XRD characterization determined that the FeCl2crystal was ferrous chloride tetrahydrate and it belonged to triclinic. Good flocculation effect obtained with the ferrous chloride dosage of2.6g/L and pH=5at the temperature of25-40℃,and the removal rates of chroma and turbidity were up to78.95%and77.24%respectively. The optimal preparation conditions of PFAC were as follows:the calcium aluminate dosage was4%, the reaction time was1h,reaction temperature was80℃, and oxidant amount (n (Fe2+):n (H2O2)) was1:1.2. Self-prepared PFAC had good flocculation effect on bamboo wastewater, and removal rate of chroma, turbidity and total phosphorus were higher than80%,while COD removal rate was up to50%. Compared with commercially available PFAC, chroma, turbidity and COD removal efficiency were better, but total phosphorus removal rate was slightly lower.Combination process of vacuum evaporation and preparation of poly Ferric was determined to be the pilot treatment process of waste hydrochloric acid pickling liquid. Take a production of2tons waste pickling liquid per day for example, using the combination process can avoid the emissions of waste pickling liquid, and will obtain income of169,400yuan per year, with good environmental and economic benefits.