Efficiency of Modified Natural Clinoptilolite Tuff for As(III) and As(V) Uptake from Model Polluted Water

Abstract

Granular and powdery clinoptilolite tuff samples from Beli Plast, Eastern Rhodopes, Bulgaria, were coated with metal hydroxides (Fe, Al, Fe-Mg) by two-step alkalization. The prepared sorbents were tested for As(III) and As(V) uptake from a modeled water solution with an arsenic concentration of 44 μg/L. The granular sorbent was used in the sorption columns and showed a high efficiency of arsenic purification from slightly polluted waters. The calculated maximum sorption capacity for the optimal conditions is 32.9 μg/g. The adsorption proceeds according to the Langmuir model. The mechanism of adsorption is most likely inner-sphere complexation. The sorbents’ complete regeneration was achieved by NaOH treatment. The results of the experiments show good possibilities for obtaining water with an arsenic concentration ranging from below the limit of detection to 3.8 µg/L, which is a significantly lower value than the permitted value of 10 μg/L and close to the national environmental quality standard for shallow waters. The high efficiency shows Fe- or Mg,Fe-coated clinoptilolite sorbents. The sorbents are highly efficient in purifying 400 liters of water with an initial concentration of 44 mg/L of either arsenate or arsenite per 1 kilogram of sorbent at a rate of 2.4–2.0 L/h/kg. The powdered sorbents used in a batch system under “static” conditions showed a much higher adsorption capacity than the granular one. Such sorbents are more suitable for small quantities of water with a high concentration of arsenic.