Geochemical Characteristics and Toxic Elements in Alumina Refining Wastes and Leachates from Management Facilities

Abstract

A nationwide investigation was carried out to evaluate the geochemical characteristics and environmental impacts of red mud and leachates from the major alumina plants in China. The chemical and mineralogical compositions of red mud were investigated, and major, minor, and trace elements in the leachates were analyzed. The mineral and chemical compositions of red mud vary over refining processes (i.e., Bayer, sintering, and combined methods) and parental bauxites. The main minerals in the red mud are quartz, calcite, dolomite, hematite, hibschite, sodalite, anhydrite, cancrinite, and gibbsite. The major chemical compositions of red mud are Al, Fe, Si, Ca, Ti, and hydroxides. The associated red mud leachate is hyperalkaline (pH > 12), which can be toxic to aquatic life. The concentrations of Al, Cl−, F−, Na, NO32−, and SO42− in the leachate exceed the recommended groundwater quality standard of China by up to 6637 times. These ions are likely to increase the salinization of the soil and groundwater. The minor elements in red mud leachate include As, B, Ba, Cr, Cu, Fe, Ni, Mn, Mo, Ti, V, and Zn, and the trace elements in red mud leachate include Ag, Be, Cd, Co, Hg, Li, Pb, Sb, Se, Sr, and Tl. Some of these elements have the concentration up to 272 times higher than those of the groundwater quality standard and are toxic to the environment and human health. Therefore, scientific guidance is needed for red mud management, especially for the design of the containment system of the facilities.

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

“…As (28.7–203 µg/g), Pb (43.7–132 µg/g), and Cr (480–1370 µg/g) were the most abundant trace elements in the samples. In addition, the total carbon contents in the combined process red mud (i.e., HN-A-C, TC = 1.6%) were higher than the red mud from the Bayer process (TC = 0.7–1.3%), which may result from the addition of the lime in limestone during the combined process [1].…”

“…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]. Approximately 0.6–2.5 tons of red mud are produced for every ton of alumina [2,3].…”

“…The leaching behavior of red mud was evaluated by field and laboratory leaching tests to assess the potential risks of red mud leachate to human health and the environment [8,9]. 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 (NO 3 − , 183.2–730.7 mg/L), and sulfate (SO 4 2− , 502.5–6593.0 mg/L).…”

“…These elements exceed the recommended groundwater quality standards of China up to 6637 times. Sun et al [1] also found that the minor and trace elements, including arsenic (As, 0.2–2.0 mg/L), chromium (Cr, 0.1–5.9 mg/L), cadmium (Cd, 12–172 μg/L), mercury (Hg, 275–599 μg/L), and selenium (Se, 525–1359 μg/L), have a concentration up to 272 times higher than the maximum contamination levels (MCLs) of groundwater quality standards of both China and the US Environmental Protection Agency (USEPA). Rubinos et al [10] evaluated the leaching behavior of trace metals from red mud using batch leaching procedures, including the toxicity characteristics leaching procedure (TCLP) and sequential leaching tests.…”

Neutralization of high pH and alkalinity effluent from recycled concrete aggregate by common subgrade soil

“…Alkaline wastes, such as RCA, fly ash, and red mud, have been extensively reused as engineering fills or additives in concrete in recent years (Abbaspour, Tanyu, & Cetin, 2016;Bestgen, Cetin, & Tanyu, 2016;Cetin, Aydilek, & Li, 2014;Gomes, Mayes, Rogerson, Stewart, Burke, 2016;Sun et al, 2019). Leachate generated from these wastes are often associated with the concerns of high pH (usually pH = 9-14) and elevated concentrations of hazardous elements, especially oxyanions (e.g., arsenic [As] and chromium [Cr]) (Chen, Bradshaw, Benson, Tinjum, & Edil, 2012;Sun et al, 2019). Attenuation options for the hyperalkaline leachate usually include active aeration (high partial pressure of CO 2 ) for carbonation, recirculation of drainage waters, and acid treatments (Abbaspour et al, 2016;Mayes et al, 2009).…”