Study On Comprehensive Utilization Of Spent Pickling Liquors From Iron And Steel Industry

Steel surface pickling process generates a considerable quantity of spent pickling liquors. Spent pickling liquors mainly contains a high concentration of free sulfuric acid ?when using sulfuric acid pickling? or hydrochloric acid ?when using hydrochloric acid pickling?,a large number of ferrous sulfate, small amounts of manganese, traces of lead, cadmium, mercury, copper, cobalt, nickel and other heavy metal ions, traces of arsenic, sulfur and other non-metallic materials. Spent pickling liquors is a kind of wastewater with strong acidity and high toxicity.Traditional method for treatment of spent pickling liquor is neutralization precipitation,which will produce sludge as secondary pollutant, but also cannot reach the purpose of recycling valuable component. Neutralization precipitation method is not in accord with the concept of modern iron and steel production of green, sustainable and circular economy, so the technology has been gradually phased out.Therefore, it is of great significance to explore the suitable methods for the treatment of spent pickling liquors.In this paper, combined with the current situation of the utilization of pickling waste liquor in domestic and foreign steel enterprises. The chemical composition analysis and removal of trace harmful impurities method of pickling waste liquid was studied in a metal product factory in Xiangtan as the research object.At the same time, the research on the preparation of iron based products by pickling waste liquor was carried out. A new process of resource treatment for steel enterprises was explored.Iron powder or metallic zinc or iron powder and metallic zinc powder mixture reduction method is used to remove trace of heavy metals and metalloid arsenic.When reduction temperature is 50-70?, reaction time is3h, iron or zinc or iron and zinc powder mixture amount is 1.2 times of free acid and total molar amount of trace heavy metals in waste water with acid.The methods for removal of lead and cadmium, copper, cobalt and nickel removal rate can reach 84.50%,68.33%,88.88%, 73.33%,77.77% respectively, the arsenic removal rate could reach 100%.The waste pickling waste liquor was used as the raw material, and the liquid polymerized ferric sulfate and the solid ferrous sulfate are prepared by polymerization and evaporation process.The quality of its products fully meet the national water treatment chemical with solid polymeric ferric sulfate product quality standards ?GB14591-2006? I level indicators.The reaction conditions as follows:nFeSO₄:nH₂SO₄=1.95-2.05, reaction temperature was 65-70?, and the total reaction time was 3.0-3.5h.The evaporation temperature was 70-85?, vacuum degree was 0.07-0.08 Mpa,evaporation concentration ratio was 1:?0.25-0.30?.At the same time, in addition to using pickling waste liquor purified by spray drying was prepared in accordance with the national standard of feed grade ferrous sulfate and ferrous sulfate solid products.