Abstract
The biodegradable polysaccharide chitosan possesses protonated and natural amino groups at medium pH values and has therefore been used as an adsorbing material for nickel salts in water treatment. Nickel is a problematic heavy metal ion which can cause various diseases and disorders in living organisms. Here, we show the influence of oxyanions (e.g., nitrate and sulfate) to the adsorption of nickel ions. Hence, simultaneously we are addressing the increasing global problem of nitrate and sulfate ion pollution in groundwater and surface water. A series of adsorption experiments was carried out in order to determine (i) the adsorption equilibrium, (ii) the adsorption capacity in dependence on the initial nickel ion concentration, and (iii) the influence of the anion presented in solution for the adsorption capacity. Surface morphology of chitosan flakes before and after the adsorption process has been studied with SEM-EDX analysis. The chitosan flakes exhibited promising adsorption capacities of 81.9 mg·g−1 and 21.2 mg·g−1 for nickel (sulfate) and nickel (nitrate), respectively. The calculated values of Gibbs free energy change ΔG0 confirm the higher adsorption of nickel ions in presence of sulfate ions. Hence, higher anion valence leads to a higher adsorption capacity.
Highlights
In recent years, heavy metal ion pollution in water treatment has become a major issue in research due to the voluminous discharge into the environment by mining activities, industrial, and agricultural effluents [1,2]
Chitosan with a degree of deacetylation of 90% is a good adsorbent for heavy metal ions in water
The dependence of the adsorption capacity of chitosan flakes for nickel ions was investigated on adsorption time, initial nickel concentration and the valence of the oxyanion
Summary
Heavy metal ion pollution in water treatment has become a major issue in research due to the voluminous discharge into the environment by mining activities, industrial, and agricultural effluents [1,2]. Guidelines, the maximum value of nickel is 4.1 mg·L−1 for industrial effluent and less than 0.1 mg·L−1 for drinking water [5]. Oxyanions like nitrate and sulfate became an increasing environmental issue as well, due to overfertilization and mining. Nitrate ions stimulate the growth of organisms and algaes and is dangerous for aquatic life [6]. The increasing amount of sulfate ions leads to a decreasing pH-value of the water and to damages and corrosion of cement in sewer and bridges for example [7]
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