Abstract
This research is aimed at investigating the possible use of cassava agroindustry solid wastes in manufacturing adsorbents and their use in removing heavy metals Cd2+, Pb2+, and Crtotal from water. Thus, a pilot study was conducted in two main steps: (1) obtaining and characterizing the adsorbents and (2) laboratory studies focused on the evaluation of critical physicochemical parameters on adsorption, such as pH of the solution containing heavy metals, the effect of adsorbent dose, besides kinetics and equilibrium adsorption and desorption studies. Three adsorbents were studied, cassava barks, bagasse, and their mixture. SEM, FTIR, pHPZC, acid digestion, and chemical composition analysis were employed for adsorbent characterization. The pH of the contaminated solution was evaluated within 4.0 to 7.0, while the adsorbent doses varied from 5.0 to 24.0 g L-1. The adsorption kinetics was evaluated within 5 to 180 minutes and interpreted using pseudofirst- and second-order models. Finally, equilibrium and desorption studies were performed by evaluating adsorbent performance within 5 to 200 mg L-1 of heavy metals, using several nonlinear models for results interpretation. SEM analysis reveals a heterogeneous structure full of cavities. FTIR before and after adsorption reveals gaps related to missing functional groups, suggesting a significant role of alkenes, carboxylic acid, alcohol, anhydride, and ether. pHPZC is found at pH 6.02, 6.04, and 6.26 for adsorbents derived from barks, bagasse, and their mixture. In low concentrations of metals, the higher adsorption capacities were found at pH 7.0 (94.9%) using 16 g L-1 of adsorbent, with the most cost-benefit dose found using 8.0 g L-1. The removal of metals reaches equilibrium within 5-10 minutes of contact time with pseudosecond-order best adjustments to the observed phenomena. The adsorption of metals by a cassava adsorbent is better adjusted to the Freundlich model, with significant and critical information provided by Sips, Redlich-Peterson, Temkin, Liu, and Khan models. Adsorption/desorption studies indicate that cassava adsorbent performs, on average, -10% of the adsorption of metals compared to activated carbon. Nevertheless, factors such as low cost and availability favor the use of such natural materials.
Highlights
In the last decade, the increasing industrialization and urbanization have raised the number of pollutants disposed of in the environment, especially water bodies [1]
WHO [2] reports that 785 million people lack even a basic drinking water service, including 144 million people who are dependent on surface water; globally, at least 2 billion people use a drinking water source contaminated with feces, that is not to mention water pollution by chemicals, such as toxic heavy metals
Among the advanced treatments that are usually employed for the removal of toxic metals, we can highlight chemical and physical precipitation, ionic exchange, Fenton and photo-Fenton processes, oxidation processes, filtration by membranes, osmosis processes, advanced oxidation processes, and adsorption with activated carbons; this last example is considered a gold standard for the removal of many organic and inorganic pollutants from waters and wastewaters [4], especially when those are in low concentrations but not low enough to ensure the safety of the disposal of the wastewater or the use of water [5–7]
Summary
The increasing industrialization and urbanization have raised the number of pollutants disposed of in the environment, especially water bodies [1]. In this sense, among the many contaminants that affect aquatic environments and human health, the pollution from organic or inorganic compounds, such as toxic metals and metalloids Among the advanced treatments that are usually employed for the removal of toxic metals, we can highlight chemical and physical precipitation, ionic exchange, Fenton and photo-Fenton processes, oxidation processes, filtration by membranes, osmosis processes, advanced oxidation processes, and adsorption with activated carbons; this last example is considered a gold standard for the removal of many organic and inorganic pollutants from waters and wastewaters [4], especially when those are in low (or trace) concentrations but not low enough to ensure the safety of the disposal of the wastewater or the use of water [5–7].
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