Abstract
Industrial and agricultural activities discharges huge amount of hazardous pollutants that lead to massive environmental pollution and health hazards. Keratin is a fascinating protein and useful biopolymer, which is usually found in wool, human hair, nails, feathers, etc. The present research deals with the potentiality of human hair towards removal of hexavalent chromium from aqueous solution through batch mode. The adsorbent was characterized by pHZPC and SEM study. The Cr(VI) adsorption was studied with the help of different process parameters, viz. initial concentration, contact time, adsorbent dose, pH, and temperature. Results revealed that Cr(VI) adsorption by human hair was highly pH sensitive. Maximum Cr(VI) was adsorbed from water at pH 1.0. Study of temperature effect on chromium adsorption confirmed the endothermic behaviour of the process. On the other hand, thermodynamic properties were also calculated and found that physisorption was dominant with activation energy of 0.385 kJ mol−1. Kinetic study revealed that pseudo-second-order model was followed by the adsorption process. Adsorption equilibrium was analysed with Langmuir, Freundlich, and Dubinin–Radushkevich isotherm models. Results showed that the adsorption system followed both Langmuir and Freundlich isotherms with Langmuir adsorption capacity of 9.852 mg g−1, which was compared with other adsorbents and observed that the performance of the present adsorbent is better than others. Finally, it can be concluded that human hair could be an alternative chief low-cost waste material for decontamination of heavy metals from an aqueous medium.
Highlights
Heavy metal-induced pollution has remarkably increased due to excessive discharges of heavy metals from various industries including metallurgical, steel manufacturing, fertilizer, including sponge iron, etc. (Rajapaksha et al 2018; Gu et al 2015)
Pseudo-first-order and intraparticle diffusion model are moderately fitted with the experimental data (Table 2). These results suggest that the adsorption onto the adsorbent at specific temperature was best presented by the pseudo-second-order equation, which is based on the assumption that the rate-limiting step may be the chemisorption (Aksu 2001)
The present study results revealed that human hair was effective in the removal of Cr(VI) from aqueous medium
Summary
Heavy metal-induced pollution has remarkably increased due to excessive discharges of heavy metals from various industries including metallurgical, steel manufacturing, fertilizer, including sponge iron, etc. (Rajapaksha et al 2018; Gu et al 2015). Chromium exists in various oxidation states including Cr(III), which is mainly presence in the aqueous medium under acidic condition Under oxidizing conditions Cr exists as Cr(VI)-oxoanion species such as HCrO4− (pH 4–6) or CrO42− (pH 8–10). The lower oxidation state of chromium can be precipitated after reduction of Cr(VI) (Hsu et al 2009). In the soil enriched with Fe and Mn oxides, Cr(VI) can be adsorbed through sorption process under acidic condition (Zhang et al 2017). Cr(VI) is a powerful oxidant which can oxidize the biomolecules and subsequently induce toxicity. The usual toxicity symptoms are necrosis, irritation of the gastrointestinal mucosa, etc. Hexavalent chromium is known for its mutagenic and carcinogenic nature (Eleftheriou et al 2015). Cr(VI) interacts with reducing biomolecules through formation of labile intermediates, and possibly this labile intermediate interacts with biomolecules including the
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