Abstract
This mini-review provides coverage of chitosan-based adsorbents and their modified forms as sustainable solid-phase extraction (SPE) materials for precious metal ions, such as gold species, and their complexes in aqueous media. Modified forms of chitosan-based adsorbents range from surface-functionalized systems to biomaterial composites that contain inorganic or other nanomaterial components. An overview of the SPE conditions such as pH, temperature, contact time, and adsorbent dosage was carried out to outline how these factors affect the efficiency of the sorption process, with an emphasis on gold species. This review provides insight into the structure-property relationships for chitinaceous adsorbents and their metal-ion removal mechanism in aqueous media. Cross-linked chitosan sorbents showed a maximum for Au(III) uptake capacity (600 mg/g), while S-containing cross-linked chitosan display favourable selectivity and uptake capacity with Au(III) species. Compared to industrial adsorbents such as activated carbon, modified chitosan sorbents display favourable uptake of Au(III) species, especially in aqueous media at low pH. In turn, this contribution is intended to catalyze further research directed at the rational design of tailored SPE materials that employ biopolymer scaffolds to yield improved uptake properties of precious metal species in aqueous systems. The controlled removal of gold and precious metal species from aqueous media is highly relevant to sustainable industrial processes and environmental remediation.
Highlights
The opportunity to design tailored materials for specific adsorption-based applications that position chitosan as an emerging renewable material for controlled recovery of precious metal-ions in aqueous media. This contribution provides a review of chitosan-based materials for their application as sorbents for solid-phase extraction (SPE) for precious metals, where the research results related to Au and Pd species covers literature over the past decade
When the Au(III) adsorption isotherms were obtained at variable temperature conditions between 25 to 35 ◦ C, the uptake capacity of Au(III) ions by the thiourea-grafted chitosan was reduced by 50% at elevated temperatures
The adsorption properties of the modified adsorbents were compared against the properties of pristine chitosan and activated carbon (Table 5)
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. In the case of pristine chitin-based sorbents such as chitosan, the adsorption properties toward cation and anion species by the pristine biopolymer have limitations due to the low surface area and limited accessibility of surface chemical groups [8,9,10]. Chitosan can be modified by various physical and chemical synthetic strategies to yield biosorbents that yield environmentally friendly SPE materials with improved adsorption properties that are cost-effective for the recovery of precious metals from aqueous media [9]. The opportunity to design tailored materials for specific adsorption-based applications that position chitosan as an emerging renewable material for controlled recovery of precious metal-ions in aqueous media This contribution provides a review of chitosan-based materials for their application as sorbents for solid-phase extraction (SPE) for precious metals, where the research results related to Au and Pd species covers literature over the past decade. Chitosan-based adsorbents are viewed to contribute favourably in specialized applications that range from environmental remediation to mineral tailings recovery of precious metals [7]
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