PH-Dependent Leaching Characteristics of Major and Toxic Elements from Red Mud

Yulong Cui,Daoping Peng,Tao Huang,Chunwei Sun,Jiannan Chen,Yibo Zhang

doi:10.3390/ijerph16112046

Yulong Cui, Daoping Peng + Show 4 more

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https://doi.org/10.3390/ijerph16112046

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Abstract

This study analyzes the leaching behavior of elements from red mud (bauxite residue) at pH values ranging from 2 to 13. The leaching characteristics of metals and contaminated anions in five red mud samples produced by Bayer and combined processes were analyzed using the batch leaching technique following the US Environmental Protection Agency (USEPA) Method 1313. In addition, the geochemical model of MINTEQ 3.1 was used to identify the leaching mechanisms of metals. The results showed that Ca, Mg, and Ba follow the cationic leaching pattern. Al, As, and Cr show an amphoteric leaching pattern. The leaching of Cl− is unaffected by the pH. The maximum leaching concentration of the proprietary elements occurs under extremely acidic conditions (pH = 2), except for As. The leaching concentration of F− reaches 1.4–27.0 mg/L in natural pH conditions (i.e., no acid or base addition). At the same pH level, the leaching concentrations of Pb, As, Cr, and Cu are generally higher from red mud produced by the combined process than that those of red mud from the Bayer process. The leaching concentration of these elements is not strongly related to the total elemental concentration in the red mud. Geochemical modeling analysis indicates that the leaching of metal elements, including Al, Ca, Fe, Cr, Cu, Pb, Mg, Ba, and Mn, in red mud are controlled by solubility. The leaching of these elements depended on the dissolution/precipitation of their (hydr)oxides, carbonate, or sulfate solids.

Highlights

Red mud refers to the industrial solid waste associated with the process of alumina smelting from bauxite ore, which mainly consists of alumina, silicate, iron, and titanium oxides [1]
Leaching controlling mechanisms of metal elements were studied via the geochemical modeling program MINTEQ 3.1
Based on the findings of this study, the following conclusions and recommendations are drawn: Acid neutralization curves for the red mud samples show a pH plateau at 2 < pH < 6, which is due to the buffering of carbonates in the red mud

Summary

Introduction

Red mud (bauxite residue) refers to the industrial solid waste associated with the process of alumina smelting from bauxite ore, which mainly consists of alumina, silicate, iron, and titanium oxides [1]. 0.6–2.5 tons of red mud are produced for every ton of alumina [2,3]. 150 million tons of red mud are produced annually worldwide, and the annual generation of red mud has grown since 2015 [4,5]. Sun et al [1] conducted a nationwide evaluation of the chemical compositions in leachates from red mud across China. They found that red mud leachate is hyperalkaline (pH > 12) and contains high concentrations of aluminum (Al, 118.3–1327.4 mg/L), chloride (Cl− , 511.4–6588.1 mg/L), fluoride (F− , 88.0–299.6 mg/L), sodium (Na, 1200.5–10,650.0 mg/L), nitrate (NO3 − , 183.2–730.7 mg/L), and sulfate (SO4 2− , 502.5–6593.0 mg/L)

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