NEW APPROACHES AND APPLICATIONS OF NATURAL ZEOLITES FOR BORON ADSORPTION FROM AQUEOUS SOLUTIONS

Abstract

Excessive mineral extraction and boric acid production can lead to elevated boron concentrations in wastewater. While boron is an essential micronutrient for humans, excessive exposure and intake can result in adverse health effects. Existing treatment processes for boron contaminated wastewater have various limitations related to effectiveness, production of additional solid waste and high operational costs. This study investigates the use of natural zeolite as a cost-effective, sustainable and environmentally friendly adsorbent for boron removal. Natural zeolites are alumosilicate porous minerals widely used in wastewater treatment applications. To enhance its adsorption properties, natural zeolite was modified using a nickel sulphate solution. In this work, four adsorbents were analyzed: raw natural zeolite, nickel-modified natural zeolite, zeolite/hydroxyapatite and nickel-modified zeolite/hydroxyapatite composite. The zeolite/hydroxyapatite composite was synthesized under hydrothermal conditions at 160 °C for 4 hours at autogenous pressure. Characterization of the adsorbents was performed using X-ray powder diffraction (XRPD), scanning electron microscopy and thermogravimetric analysis. XRPD analysis confirmed clinoptilolite as the dominant mineral phase in the zeolitic tuff and showed that hydrothermal treatment did not affect its crystallinity. The adsorption properties were tested using a synthetic boron solution at pH 9, where boron exists in both B(OH)₃ and B(OH)₄^– forms.  The results showed that the presence of nickel primarily on the surface of the adsorbent leads to an increase in boron adsorption, which is a consequence of its ability to form complexes with B(OH)₄^–. This research confirmed that adsorbents based on metal-saturated natural zeolite are promising adsorbents of boron compounds from wastewater.