Abstract Dealkalization is a major limiting factor for the comprehensive utilization of red mud, and acid leaching is considered an effective and promising way to achieve it. Most studies have focused on the recovery of metals in this extreme alkaline waste by strong acid leaching, ignoring the dealkalization and stabilization of red mud with low concentrations of acid. In this study, the leaching behavior of the major elements in red mud was carefully investigated by the treatment with a range of H+ concentrations from 10−6 to 1.8 mol/L. Analysis of both leachate and residue confirmed a stepwise sequential leaching behavior of Na, Al, and Ca, which was important for dealkalization of red mud. Treatment with an acidic solution at pH 1 removed 17.84% of Na, but almost no other metals. Greater than 60% Na was leached by an acidic solution with H+ concentration of 0.5 mol/L, but the dissolution efficiencies of Al, Si, and Ca were less than 10%, resulting in a relatively simple leaching liquid treatment process. And the pH of the leaching residue was 8.5 which slightly alkaline so the residual RM could be used as soil aggregates. When using an acidic solution with an H+ concentration of 1.6 mol/L, the dissolution efficiency of Na reached at 94.70%, leaving only 0.47% Na in the residue, which makes it possible to meet the demand of application for construction materials. From the results of the phase analysis, it was found that the sequential leaching behavior was due to the dissolution, decomposition, and transformation of the particles containing the main elements, and was compatible with the SEM-EDS inspection. Based on these results, a new multi-stage acid leaching dealkalization process has been proposed to provide an effective and economical way to dealkalize red mud.

中文翻译：

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弱酸脱碱过程中赤泥的分级浸出行为

摘要 脱碱是赤泥综合利用的主要限制因素，酸浸被认为是实现脱碱的有效途径。大多数研究都集中在通过强酸浸出来回收这种极端碱性废物中的金属，而忽略了低浓度酸对赤泥的脱碱和稳定作用。在本研究中，通过用 10-6 至 1.8 mol/L 的 H+ 浓度范围进行处理，仔细研究了赤泥中主要元素的浸出行为。对浸出液和残渣的分析证实了 Na、Al 和 Ca 的逐步顺序浸出行为，这对赤泥脱碱很重要。用 pH 值为 1 的酸性溶液处理去除了 17.84% 的 Na，但几乎没有其他金属。大于60%的Na被H+浓度为0.5 mol/L的酸性溶液浸出，但Al、Si和Ca的溶解效率小于10%，因此浸出液处理工艺相对简单。浸出残渣的pH值为8.5，呈微碱性，残渣可用作土壤团聚体。当使用H+浓度为1.6 mol/L的酸性溶液时，Na的溶解效率达到94.70%，残留物中仅剩下0.47%的Na，可以满足建筑材料的应用需求。从物相分析结果发现，序贯浸出行为是由于含有主要元素的颗粒的溶解、分解和转化，与SEM-EDS检测相适应。