Resource Reutilization Of Steel Pickling Liquors:Hydrochloric Acid Regeneration And Poly-ferric Coagulant Preparation

Steel Spent Pickling Liquors (SPL) in most small-scale steel plants are commonly treated by neutralization-precipitation, or entrusted to deal with by the hazardous waste institutes. However, the disposal of hydroxides sludge, treatment cost and the waste of resource limit the application. SPL regeneration is regarded as one of the best available techniques.A new method of SPL regeneration was presented, a combination process of salt-added distillation and preparation of coagulants from the distillation residue to regenerate acid and iron. Firstly, the liquor was distilled after mixture of CaCl2and SPL, the regenerated acid was recycled by condensation, and then the non-condensable hydrogen chloride was scrubbed; finally, the distillation residue was prepared into iron-based coagulants. These following aspects are focused:(1) The effects of chloride salts on hydrochloric acid distillation were studied, including KC1, NaCl, CaCl2, MgCl2, FeCl2, FeCl3. The results showed that CaCl2and MgCl2had the most promotion of HCl-H2O relative volatility. There were no insignificant differences between addition of CaCl2and MgCl2when distillation. In addition, when dosage was more than lmol/L, there was little increase of recycled acid concentration. What’s more, more massive non-condensable hydrogen chloride generated when addition of MgCl2, which increased the load of exhaust treatment. And CaCl2is cheaper, CaCl2would be the better alternative.(2) The effects of distillation operation on inorganic coagulate preparation were studied. The results indicated that OH/Fe mole ratio values were qualified when distillation ratio were30%at least, and prepared coagulants with30%distillation ratio presented the best coagulation performances. The distribution of Fe species was analyzed by Fe-Ferron complexation timed spectrophotometry, which illustrated distillation ratio had influences on Fe species distribution.(3) Simulated dyeing wastewater and real dyeing wastewater coagulation jar-tests were conducted. For simulated wastewater, the color of direct dye was very easily removed, and acid dye was hard to remove. For real dyeing wastewater, which origin sample CODCr was1375mg/L and colority was500times, the CODCr and colority removal effiency was48%and87%, respectively.(4)2t/d SPL treatment program was designed. The main equipments included hydrogen chloride distillation tower, stirred tank reactor, condenser, scrubber and so on, all the equipments would be fabricated with anti-corrosive material, such as graphite material, graphite modified polypropylene material or polypropylene plastic material. Engineering economic analysis results indicated that the direct economic benefits of the program was￥11800/a, the indirect economic benefits was￥160000/a approximately.