Pickling is a common pre- or intermediate treatment in electroplating, enamelling, rolling and other processes. Here, pickling sludge was converted to a novel product of KFeS₂ nanorods via a facile hydrothermal method that effectively removes heavy metals from electroplating wastewater. The pickling sludge was a mixture of weakly crystallised Fe in the form of irregular aggregates. The Fe content of the raw sludge was 35.9 wt% and the main impurities included aluminium, carbon and salt. After hydrothermal treatment, 74.6% of the Fe-containing compounds were converted to KFeS₂ nanorod clusters with a diameter of 300 nm and lengths in the range of 2–5 μm. In the hydrothermal system, Fe³⁺ was dissolved from the surface of the pickling sludge to form Fe(OH)₄⁻, which accelerated the formation of KFeS₂ nanorod clusters. The prepared KFeS₂ nanorods were effective in treating raw electroplating wastewater at pH 12.1, with removal rates of over 99% for Zn and Cu and 63.3% for Ni. These values were higher than those of poly ferric sulphate, poly aluminium chloride, Na₂S, raw sludge and activated carbon powder. The KFeS₂ nanorods were metastable and hydrolysed spontaneously in alkaline electroplating wastewater. The generated Fe–SH groups on the surface formed a complex with metals, namely, Cu, Zn and Ni, and thus were removed with flocculation. Therefore, the KFeS₂ nanorods generated from pickling wastewater recycling could be used as a prospective coagulant for heavy-metal removal in the treatment of alkaline electroplating wastewater.

中文翻译：

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一种从酸洗废水中回收铁的新方法，产生 KFeS2 晶须用于电镀废水处理

酸洗是电镀、搪瓷、滚压等工艺中常见的前处理或中间处理。在这里，酸洗污泥通过简便的水热法转化为 KFeS ₂纳米棒的新型产品，可有效去除电镀废水中的重金属。酸洗污泥是不规则聚集体形式的弱结晶铁的混合物。原料污泥的Fe含量为35.9wt%，主要杂质为铝、碳和盐。水热处理后，74.6% 的含铁化合物转化为 KFeS ₂纳米棒簇，直径为 300 nm，长度为 2-5 μm。在热液系统中，Fe ³⁺从酸洗污泥的表面溶解形成 Fe(OH) ₄ ^-，这加速了 KFeS ₂纳米棒簇的形成。制备的 KFeS ₂纳米棒在 pH 12.1 时可有效处理电镀原废水，对 Zn 和 Cu 的去除率超过 99%，对 Ni 的去除率为 63.3%。这些值高于聚合硫酸铁、聚合氯化铝、Na ₂ S、原料污泥和活性炭粉的值。KFeS ₂纳米棒在碱性电镀废水中是亚稳态和自发水解的。表面生成的 Fe-SH 基团与金属形成络合物，即 Cu、Zn 和 Ni，从而通过絮凝去除。因此，KFeS ₂ 酸洗废水回收利用产生的纳米棒可用作碱性电镀废水处理中去除重金属的预期混凝剂。