Improvement of alkaline electrochemical characteristics of bauxite residue amendment with organic acid and gypsum

Abstract

Neutralization of alkaline properties of bauxite residue (BR) by using organic acid and gypsum additions may effectively improve electrochemical properties and alleviate physicochemical barriers to ecological rehabilitation. Mineral acids, citric acid and hybrid acid–gypsum additions were compared for their potential to transform and improve zeta potential, isoelectric point (IEP), surface protonation and active alkaline —OH groups, which are critical factors for further improvement of physicochemical and biological properties later. Isoelectric points of untransformed bauxite residue and six transformed derivatives were determined by using electroacoustic methods. Electrochemical characteristics were significantly improved by the amendments used, resulting in reduced IEP and —OH groups and decreased surface protonation for transformed residues. XRD results revealed that the primary alkaline minerals of cancrinite, calcite and grossular were transformed by the treatments. The treatments of citric acid and gypsum promoted the dissolution of cancrinite. From the SEM examination, citric acid and gypsum treatments contributed to the reduction in IEP and redistribution of —OH groups on particle surfaces. The collective evidence suggested that citric acid and gypsum amendments may be used firstly to rapidly amend bauxite residues for alleviating the caustic conditions prior to the consideration of soil formation in bauxite residue.

摘要

本文开展了有机酸-石膏联合转化赤泥碱性电化学性能的研究,探究了有机酸-石膏作用过程中 zeta 电位、等电点、矿物表面质子化、表面碱性官能团—OH 的转变及其对赤泥堆场生态修复相关理 化性质的影响。为了更好地评价有机酸的转化效果,利用无机酸(盐酸、硫酸)进行对比分析。采用 有机酸-石膏中和赤泥的碱性,可有效改善赤泥的碱性电化学性能,处理后的赤泥等电点和矿物表面 质子化程度显著降低,矿物颗粒表面碱性官能团—OH 的含量也明显减少。XRD 结果揭示有机酸、无 机酸、酸-石膏联合转化了赤泥中主要的碱性物相钙霞石、方解石、钙铝榴石,但有机酸-石膏联合作 用进一步促进了钙霞石的溶解。从SEM 图可以看出,有机酸-石膏联合作用改善了赤泥颗粒的分布, 也有利于等电点的降低及矿物颗粒表面碱性官能团—OH 的重新分布。有机酸-石膏联合调控赤泥碱性 的效果非常显著,可进一步促进碱性的转化,对实现堆场赤泥的土壤化具有重要的作用。