Sorption Properties of Freshly Precipitated Iron(III) Hydroxide toward Nickel Ions. Part 1. Mechanism and Efficiency of the Sorption Process

The present work demonstrates that the use of iron(III) hydroxide as a sorbent fabricated by precipitation from a solution of iron(III) chloride can purify contaminated solutions from toxic nickel ions. The study was performed at room temperature on a model of solution of sodium sulfate (400 mg/L) simulating polluted natural and wastewater. It has been shown that the removal of nickel ions from the model solution by iron(III) hydroxide precipitate at pH 7 and 8 is described with a satisfactory accuracy by the classical adsorption isotherms of Freundlich, Langmuir, and Dubinin–Radushkevich. Low values of the free energy of adsorption that do not exceed 8 kJ/mol indicate the physical nature of adsorption and exclude ion-exchange interaction of nickel ions with iron(III) hydroxide. The most complete removal of nickel ions from the solution occurs during the sorption with iron(III) hydroxide at pH 8. The sorption capacity of iron(III) hydroxide toward nickel ions at both pH 7 and 8 is almost an order of magnitude higher than the same value for many mineral, carbon, and coal sorbents. During the sorption process at pH 7, the adsorption capacity of iron(III) hydroxide precipitates decreases along with the increase of the initial concentration of iron(III) ions in solution, whereas during sorption at pH 8, on the contrary, it remains constant and does not depend on the initial concentration of iron(III) ions in the solution. The obtained data enable one to select the concentration of iron(III) hydroxide precipitate required to achieve a preset depth of purification of contaminated solutions from nickel ions.