Removal of Zn 2+ and SO 4 2− from aqueous solutions on acidic and chelating dehydrated carbon

Abstract

The agricultural waste, date palm leaflets, was carbonized chemically using sulfuric acid treatment. Produced dehydrated carbon (DC) was subjected to surface functionalization using ethylene diamine producing chelating dehydrated carbon (CDC). In the process, ∼80 % of the carboxylic content on DC was converted to amide successfully. DC acts as a cation exchanger because of the high content of carboxylic groups on its surface showing acidic nature. However, CDC possesses amine and amide groups showing basic nature. Both amine and amide groups are capable of chelating Zn²⁺ at high pH; however, at low pH, the amine group becomes protonated acting as anion exchanger. Sorption of Zn²⁺ and SO₄²⁻ was investigated in terms of contact time, initial pH, concentration, and carbon reuse. Zn²⁺ shows maximum sorption at initial pH 5; however, maximum sorption of SO₄²⁻ takes place at initial pH 2. Kinetic and equilibrium studies were carried out at initial 5 and 2 for Zn²⁺and SO₄²⁻, respectively. Sorption kinetics data follow well the pseudo second-order model. The equilibrium sorption data follow the Langmuir isotherm more than the Freundlich isotherm. CDC shows better sorption performance for Zn²⁺ and SO₄²⁻ than DC. DC and CDC show combined equimolar removal of both Zn²⁺ and SO₄²⁻ at initial pH 2.3 and 2.6, respectively, with efficient recycle properties. Combined removal of Zn²⁺ and SO₄²⁻ from spiked municipal wastewater shows less uptake on both carbons than from deionized water.

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