Dealkalization of Red Mud by Mild Acid Leaching and Comprehensive Utilization
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摘要:
强碱性是制约赤泥综合利用的关键因素，酸浸是实现赤泥脱碱的有效方法。大部分研究采用强酸浸出赤泥实现重金属的回收，忽略了低浓度酸对赤泥脱碱化的影响。本文研究了低浓度的硫酸浸出赤泥过程中钠的浸出行为，同时考察了硫酸浓度、液固比、搅拌速度、浸出温度和浸出时间对赤泥脱碱化的影响。结果表明：采用pH 1的酸性溶液可以浸出赤泥中17.84%的钠。采用H+浓度为0.5 mol/L的酸性溶液可以浸出赤泥中大于60%的钠，这使得浸出液处理工艺相对简单，同时滤渣的pH值为8.5，为弱碱性，可直接用于土壤。在H+浓度为1.6 mol/L、固液比为1/4 g/mL、搅拌速度为300 r/min、浸出温度为298 K和浸出时间为10 min的最佳条件下，钠的浸出率为94.70%，滤渣中只剩下0.6% 的钠，可以用于建筑材料。并对硫酸浸出动力学进行了研究。结果表明：在较低浓度的硫酸介质中，钠的浸出过程主要受产物层扩散模型控制，浸出过程的表观活化能为16.99 kJ/mol。XRD分析结果证实方解石与硫酸反应生成硫酸钙微溶物质是形成产物层的主要原因。基于上述结果，提出了一种新型多级酸浸脱碱工艺，为赤泥的综合利用奠定了基础。
Abstract:Strong alkalinity is the key factor restricting the comprehensive utilization of red mud and acid leaching is an effective method for the dealkalization of red mud. 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 Na in red mud with low concentration of sulfuric acid was carefully investigated and the effects of sulfuric acid concentration, liquid-solid ratio, stirring speed, leaching temperature and leaching time on red mud dealkalization were investigated. The results show that treatment with an acidic solution at pH 1 removed 17.84% of Na. Greater than 60% Na was leached by an acidic solution with H+ concentration of 0.5 mol/L, 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. Under the optimal conditions of H+ concentration 1.6 mol/L, solid-liquid ratio 1/4 g/mL, stirring speed 300 r/min, leaching temperature 298K and leaching time 10 min, the dissolution efficiency of Na reached at 94.70%, leaving only 0.6% Na in the residue, which makes it possible to meet the demand of application for construction materials. We also investigated the sulfuric acid leaching kinetics. The results show that the sodium leaching process is mainly controlled by the product layer diffusion model and the apparent activation energy of the leaching process is 16.99 kJ/mol in low concentration sulfuric acid medium. XRD analysis shows that calcite reacts with sulfuric acid to form calcium sulfate microsoluble substance is the main reason for the formation of product layer. Based on the above results, a new multistage acid leaching process was proposed, which laid a foundation for the comprehensive utilization of red mud.
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Key words:
- red mud /
- sulfuric leaching /
- dealkalization /
- kinetics mechanism
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表 1 赤泥的主要化学组成
Table 1. Main chemical compositions of red mud
/% 元素 Al2O3 CaO Fe2O3 TiO2 Na2O SiO2 含量 20.49 2.46 48.01 5.77 9.14 14.66 
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表 2 浸出渣的主要化学成分
Table 2. The main chemical composition of the leached residue
元素 Na Al Si Ca 含量/% 0.60 9.60 1.54 2.17
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表 3 水泥和赤泥滤渣成分对比
Table 3. The composition of cement and red mud residual
物质 Na2O/% Al2O3/% SiO2/% CaO/% 水泥 < 1 4-7 20-24 62-67 赤泥滤渣 0.47 17.8 12.8 2.5
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