Abstract
The use of heavy metals in technological applications has led to detrimental effects on human health and the environment. Activated carbon and ion-exchange resins are commonly used to remove pollutants but they are expensive. Therefore, the research of low-cost alternatives derived from natural resources and organic wastes is being considered. The aim of this study considers the use of Calcium Alginate/Spent Coffee Grounds (CA–SCGs) composite beads to adsorb heavy metals from aqueous solutions, particularly, the removal of Ni2+ or Cd2+ at concentrations from 10 ppm to 100 ppm. CA–SCGs beads were made of equal proportions of alginate and spent coffee grounds and compared with calcium alginate beads (CA beads) and spent coffee grounds (SCGs) in terms of capacity and rate of adsorption. Three cycles of adsorption/desorption were done. The beads were characterized by Scanning Electron Microscopy coupled with an energy-dispersive X-ray spectroscopy (SEM–EDX), Fourier-transform infrared spectroscopy (FT–IR), Raman spectroscopy, and point of zero charge. Langmuir, Freundlich, and Sips models, and a pseudo-second-order kinetic equation were used. Sips model showed the best correlation with the adsorption of CA–SCGs beads with capacities of adsorption of 91.18 mg/g for cadmium and 20.96 mg/g for nickel. CA–SCGs beads had a greater adsorption than the CA beads, achieving adsorption percentages close to 100% than alginate alone, showing their effectiveness in heavy metal removal.
Highlights
Heavy metals can be described as metallic elements that have a relatively high density compared to water, but the definition includes metalloids, such as arsenic
Sips model showed the best correlation with the adsorption of Calcium Alginate/Spent Coffee Grounds (CA–spent coffee grounds (SCGs)) beads with capacities of adsorption of 91.18 mg/g for cadmium and 20.96 mg/g for nickel
The International Agency for Research on Cancer (IARC) has determined that some nickel compounds are carcinogenic to humans and that metallic nickel may possibly be carcinogenic to humans
Summary
Heavy metals can be described as metallic elements that have a relatively high density compared to water, but the definition includes metalloids, such as arsenic. Synthetic mineral adsorbents made from waste material such as zeolite synthetized from fly ash product of power generation by coal (copper sorption of 4.99 mg/g) is another example of a raw material without additional applications [7] Accessible clay minerals such as glauconite (cadmium sorption of 2.596 mg/g) have the advantage that are natural, locally available, commonly occurring materials and could be reused as a sustainable and environment-friendly building material [8]. The larger adsorption by CA–SCG beads in comparison to the CA beads was seen in the lower range of concentrations (10 to 30 ppm) At these concentrations, the percentages of adsorption were closer to 100% versus the CA alone, approaching the goal of total metal removal from the water [17]. The aim of this research was to study the performance of the CA–SCGs beads in the removal of Ni2+ or Cd2+ from water at concentrations from 10 ppm to 100 ppm
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