Removal of heavy metals (Co, Cr, and Zn) during calcium–aluminium–silicate–hydrate and trioctahedral smectite formation

Abstract

Hydrated aluminosilicates were synthesized with and without aqueous heavy metals (Me), such as cobalt (Co), chromium (Cr), and zinc (Zn), by a sol-gel process at different initial molar ratios of Ca/(Si ? Al) (0.6-1.6) and Me/Si (0.0-2.0), and constant Al/Si ratio (0.05) using equilibrium-approaching experiments. The chemical composition of the reactive solutions during aluminosilicate precipitation and maturation was monitored by ICP-OES. The mineralogy, nanostructure, and chemical composition of the precipitates were studied by XRD and high-resolution TEM. At Me/Si ratios B 0.2, calcium-aluminium-silicate-hydrates (C-A-S-H) with a defect 14 Å tobermorite-like structure formed, whereas at a Me/Si ratio of 2.0, either trioctahedral Co-and Zn-smectite or amorphous Cr gels precipitated, independent of the initial Ca/(Si ? Al) ratio used for gel synthesis. The immobilization capacities for Co 2þ , Cr 3þ , and Zn 2þ by C-A-S-H, Cr gel, and trioctahedral smectite are 3-40 mg/g, 30-152 mg/g, and 122-141 mg/g, respectively. The immobilization mechanism of heavy metals is based on a combination of isomorphous substitution, interlayer cation exchange, surface (ad)sorption, and surface precipitation. In engineered systems, such as underground concrete structures and nuclear waste disposal sites, hydrated aluminosilicates should exhibit a high detoxication potential for aqueous heavy metals.

Removal of Barium from Solution by Natural and Iron(III) Oxide-Modified Allophane, Beidellite and Zeolite Adsorbents

“…The accumulation and overconcentration of hazardous metal ions in the aquatic and terrestrial environments of the Earth is a major threat for the ecological system and for human health, as most metal ions are non-biodegradable and tend to cumulate in living organisms, causing diseases and disorders [ 1 , 2 , 3 , 4 ]. In the last decades, intense research has been carried out to find advanced and economically attractive solutions, either for the complete elimination of critical metal ions from wastewater or for a concentration reduction below permissible limits set by the local and international standards [ 5 , 6 ].…”

Stabilization of heavy metals in municipal solid waste circulating fluidized bed incineration fly ash by fusion–hydrothermal method

“…According to previous literatures [9,12,13], the heavy metals could be stabilized in zeolite-like structures that were formed during the hydrothermal process. The XRD [18] characterizations and the analysis on crystal phase were conducted to demonstrate the zeolite formation during the MHP and FMHP treatments.…”

“…The zeolites formed during the hydrothermal process could improve immobilizing heavy metals in the fly ashes [9,23,24]. It is because the heavy metals that dissolved from the solid fly ash could be trapped in the zeolite frameworks through physical/chemical adsorption, ion exchange, and physical encapsulation when the zeolites are assembling [12,13]. As discussed before, the alkaline-assisted fusion process could promote the transformation of silicon and aluminum contents from crystal phase to amorphous form, as well as silicate and aluminate salts, which eventually accelerated the dissolution of Si-and Al-containing materials and then benefited the zeolite fabrication.…”

“…Bayuseno [9] reported that the heavy metals leaching from the fly ash could be reduced after hydrothermal process for 48 h. The improved performance of heavy metal stabilization was considered as the contribution of zeolite materials forming during the hydrothermal process. According to prior literatures [12][13][14], zeolites owned porous structures and high thermal and chemical stability, where heavy metals could be immobilized by various means, such as adsorption, ion exchange, and physical encapsulation. Therefore, increasing the formation of zeolites could be one of the effective methods to reduce the heavy metal pollution leaching from the MSWI fly ash.…”

Synthesis of Zeolites from Fine-Grained Perlite and Their Application as Sorbents

“…Anthropogenic activities, such as mining, transportation, agriculture, households, industry and urbanization, have led to a significant accumulation of environmentally critical heavy metal ions (Me: Cd 2+ , Cr 3+ , Cu 2+ , Fe 2+ , Mn 2+ , Ni 2+ , Pb 2+ , Zn 2+ etc.) in most of the aquatic and terrestrial environments of the Earth's surface [1][2][3][4]. These Me ions can be hazardous and health-damaging for human beings and for the ecological system, causing diseases and disorders in living organisms even at low concentrations.…”