Carbonate Coprecipitation for Cd and Zn Treatment and Evaluation of Heavy Metal Stability Under Acidic Conditions

Abstract

Mining wastes or combustion ash are materials of high carbon sequestration potential but are also known for their toxicity in terms of heavy metal content. To utilize such waste materials for engineered carbon mineralization purposes, there is a need to investigate the fate and mobility of toxic metals. This is a study of the coprecipitation of metals with calcium carbonate for environmental heavy metal mitigation. The study also examines the stability of precipitated phases under environmentally relevant acid conditions. For a wide range of cadmium (Cd) and zinc (Zn) concentrations (10 to 5000 mg/L), induced coprecipitation led to greater than 99% uptake from water. The calcium carbonate phases were found to contain amounts as high as 9.9 wt % (Cd) and 17 wt % (Zn), as determined by novel synchrotron techniques, including X-ray fluorescence element mapping and three-dimensional (3D) nanotransmission X-ray microscopy (TXM). TXM imaging revealed first-of-a-kind observations of chemical gradients and internal nanoporosity within particles. These observations provided new insights into the mechanisms leading to the retention of coprecipitated heavy metals during the dissolution of calcite in acidic (pH 4) solutions. These observations highlight the feasibility of utilizing carbonate coprecipitation as an engineered approach to the durable sequestration of toxic metals.

Maximising the benefits of calcium carbonate in sustainable cements: opportunities and challenges associated with alkaline waste carbonation

“…Direct carbonation, however, only converts the surface layer of the waste into carbonates, leaving a significant proportion of the waste's core unchanged. This poses several technical and environmental challenges to utilising such materials in sustainable cements: (i) hazardous elements may exhibit elevated leaching after carbonation 55 , both during the process and within the cement matrices; (ii) impurities can affect the polymorphisms of calcium carbonate and their transformations during carbonation, storage and utilisation 31,45 ; (iii) the carbonated layer may contain different elements from the raw wastes 15 , with varying chemical and mineralogical compositions 56 , that may interact with cement phases differently; and (iv) different sizes of the waste powders exhibit different carbonation degrees and the chemical/mineralogical heterogeneity 46 can result in different effects on the cement properties.…”

“…On the other hand, numerous research and application opportunities exist to enhance sustainability within the construction industry. These include but are not limited to (i) developing advanced in-situ analytical techniques to monitor the waste carbonation and cement hydration processes 57 ; (ii) controlling the characteristics of the carbonation layer to improve the performance of cements; (iii) combining CCS, hazardous materials treatment and resource recovery as a low-carbon remediation technology 15 ; and (iv) exploring the synergy between carbonated wastes and other supplementary cementitious materials for either better cement performance or higher efficiency of waste treatment. It is evident that addressing these challenges necessitates interdisciplinary collaborations and multiscale mechanistic studies to advance our scientific understanding of process chemistry, thermodynamics, reaction kinetics and mass transfer in different heterogeneous systems.…”

“…As depicted in Fig. 1, calcium carbonate has the capability of incorporating a substantial proportion of divalent ions 15,16 and its solubility spans over three orders of magnitude with varying dissolution kinetics, which would significantly affect their interactions with other phases in cements.…”

Recent advances of silicate materials for wastewater treatment: a review

“…The accumulation of heavy metal ions and organic pollutants in rivers stimulates the growth of microorganisms, thereby disrupting the balance of entire ecosystem [5][6][7][8]. Over the past few decades, a variety of methods have been used to eliminate wastewater pollution, including coagulation, ultrafiltration, coprecipitation, etc [9][10][11]. Nevertheless, these methods often require a large amount of costs and complex operational requirements [12,13].…”

A hybrid machine-learning approach for analysis of methane hydrate formation dynamics in porous media with synchrotron CT imaging

“…This can be observed, for instance, in materials science and geology: low-contrast phases observed in CT imaging of carbonate samples (Alqahtani et al, 2022) and carbon/epoxy woven composites (Sinchuk et al, 2020). Other examples include nano-CT in battery research (Hallot et al, 2022) or chemical science (Kim et al, 2023). Fast segmentation procedures can aid in localizing regions of interest and selecting time intervals for studying dynamic phenomena, as well as providing quantitative estimations of sample components for input into digital rock physics simulations (Wang et al, 2015;Sell et al, 2016).…”