不锈钢在生产和加工过程中表面会形成一层黑色的氧化层，需要进行酸洗去除氧化皮，在酸洗过程会产生大量的酸洗废水。2018年全球不锈钢产量达到5072.9万吨(International Stainless Steel Forum, ISSF)，每酸洗1 t不锈钢将产生1~3 m3不锈钢酸洗废水，即2018年酸洗废水产量高达5050~15300万立方米。废水中含有大量的氟离子和重金属离子需要无害化处置，同时也具有很高的资源化利用价值。酸洗废水通常用钙中和沉淀法处理，中和得到的酸洗污泥属于危废（HW17）。酸洗污泥处理方式主要有固化、填埋、热处理等，普遍存在解毒不彻底，资源化程度低，还原温度高、能耗大等问题。 本课题旨在开发一种不锈钢酸洗废水无害化资源化新工艺。该工艺基于钙钠协同中和沉淀、金属化还原、磁选分离等技术，为不锈钢酸洗废水脱氟和有价元素的高效资源化利用提供了一条新途径。主要工作如下：(1)系统研究了不锈钢酸洗废水钙钠协同中和沉淀的规律及机理。查明了CaO加入量与氟离子去除率的关系，以及金属离子去除与pH的关系，查明了单独使用CaO中和酸洗废水产生污泥量大的原因，开发了不锈钢酸洗废水钙钠协同沉淀新工艺，污泥产生量减少了14.79%，实现了废水的重金属和氟离子的达标排放。(2)采用煤基金属化还原-磁选分离技术处置中和污泥，得到铁、铬、镍合金粉末和再生萤石矿，一步工艺实现了不锈钢酸洗污泥的无害化和资源化。重点研究了还原剂用量、还原温度、还原时间、磨矿细度等条件的影响。研究结果表明，在温度1200℃、还原时间3 h、还原剂添加量15%时，可以实现铁铬镍的完全金属化还原，渣铁磁选分离后，可以得到金属品位93.62%的合金粉末，其中Fe、Cr、Ni品位分别达69.31%, 7.6%和16.71%，相应的回收率分别高达95.30%, 88.7%和97.53%。(3)系统研究了不同因素对金属合金颗粒长大的影响，包括助熔剂Na2CO3的用量、压块的压力、还原剂用量、还原温度、还原时间等。结果表明，污泥压块、添加助熔剂、增加还原剂用量、提高还原温度、延长还原时间都能促进金属颗粒的长大，因而有助于后续的金属相与非金属相的磨矿-磁选分离。(4)查明了污泥中Cr元素完全金属化还原规律和机理。通过Fe、Cr、Ni的还原热力学，对比相应的实验结果，发现污泥中Cr完全金属化温度低于理论值和文献报道的还原温度，确定了还原过程中Fe与Cr的协同促进作用，以及CaF2的助熔作用，降低了铬金属化还原的温度，实现了低温下Cr元素的完全金属化还原。(5)对整个工艺过程进行了环境影响分析。中和水达标排放及含氟尾矿的浸出毒性实验结果表明，整个工艺节能、安全、绿色，是一条资源化利用不锈钢酸洗污泥的有效新工艺。;During the production processing of stainless steel, a black oxide layer will be formed on the surface of stainless steel. It is necessary to remove the oxide layer on the surface of stainless steel by pickling. After pickling, the surface of stainless steel will be washed, pickling wastewater was produced. Global stainless steel production in 2018 reached 50.72 million tons (from International Stainless Steel Forum, ISSF), per ton of pickling stainless steel can produce 1~3 cubic meters (m3) stainless steel pickling waste water, is expected to reach 50.5 ~ 153 million cubic meters of pickling waste water. Pickling wastewater is usually treated by calcium neutralization precipitation method, the pickling sludge is hazardous waste (HW17). The neutralization sludge treatment technology mainly includes solidification, landfill, heat treatment and so on. High temperature reduction has the problems of high reaction temperature and high energy consumption.The purpose of this work is to develop a new process of harmless treatment and recourse utilization of stainless steel pickling wastewater. Based on the technologies of calcium and sodium synergistic neutralization and precipitation, direct reduction and magnetic separation, this process provides a new way for the efficient utilization of metallic elements and fluorine in the stainless steel pickling wastewater. The main work is as follows:(1) The process and mechanism of calcium - sodium synergistic neutralization was systematically studied. The relationship between CaO content and fluorine ion removal rate and pH, as well as the relationship between metal ion removal and pH were explored, the reason for the large production of neutralizing sludge was founded. Developed a new process of treatment of pickling wastewater by calcium and sodium co-precipitation, reduced the sludge production by 14.79%. and realized the standard discharge of wastewater. (2) The direct reduction and magnetic separation process of coal-based medium was adopted to realize the one-step harmlessness and resource recovery of stainless steel pickling sludge, Iron, chromium and nickel alloy powder and regenerated fluorite ore were obtained by reduction, fine grinding and magnetic separation of sludge produced through the new process of calcium and sodium Co-precipitation. The effects of dosage of reductant, reduction temperature, reduction time and grinding fineness were studied. The results show that the metallization and reduction of Fe-Cr-Ni at 1200 ℃was carried out, with 3h reductant time and 15% dosage of reductant. The alloy powders which with the metal grade of 93.62% (mass fraction) and the regenerated fluorite were obtained. The grades of Fe、Cr、Ni in the alloy powders reached 69.31%(mass fraction), 7.6%(mass fraction) and 16.71%(mass fraction), respectively. The recovery rates were as high as 95.30%, 88.7% and 97.53%, respectively.(3) The factors affecting the growth of metal alloy particles were systematically studied, including the melting effect of flux Na2CO3, the pressure of building blocks, the dosage of reductant, the reduction temperature, the reduction time and so on. The Results showed that sludge briquetting, adding flux, increasing dosage of reductant, increasing reducing temperature and prolonging reducing time can promote the growth of metal particles, thus contributing to the subsequent grinding separation of metallic phase and non-metallic phase, among which the reduction temperature and the amount of flux have the most obvious influence on the growth of metal particles. from 6 μm at lower temperature to about 200 μm at the optimal condition.(4) The regularities and mechanism of Cr reduction in sludge were found out. Through the reduction thermodynamics analysis of Fe, Cr and Ni, the corresponding test results were compared, and it was found that the complete metallization temperature of Cr in sludge was lower than the reduction temperature reported in theory and literature. The synergistic promotion effect of Fe and Cr in the reduction process was determined, which can reduce the reduction temperature of chromium and realize the low-temperature complete metallization and reduction of Cr elements.(5) The whole process was analyzed. The results showed that the neutralization water was standard discharge and the leaching toxicity of fluorine-containing tailings , the whole process is energy-saving, safe, green, which is an effective new process to utilize stainless steel pickling sludge.