Kaolin–Fly Ash Composite for Pb2+ and AsO43− Adsorption from Aqueous System

The expected benefit of composite adsorbents generally consists in their growing applicability, thanks to the combination of the adsorption properties of individual components. Composite adsorbents were prepared as mixtures of kaolin from a Czech deposit (kaolin Sedlec, SK) and two fly ashes (FAs) from a fluidised bed boiler in Czech operations differing in fuel type. The mixtures of SK with FA in a ratio of 50:50% wt. were prepared at 20 °C, 65 °C, and 110 °C in an autoclave. The source materials and composite adsorbents were tested for the adsorption of lead as Pb2+, and arsenic as AsO43− from model solutions in laboratory conditions. The adsorption of Pb2+ proceeded quantitatively on the source materials except SK, and on both the composites, with an adsorption yield of >97% and a low adsorbent consumption (~2 g.L−1). The AsO43− adsorption proceeded selectively only on both FAs, with an adsorption yield of >97% again. The adsorption of AsO43− on the composite adsorbents achieved a worse yield (˂80%), with about ten times more adsorbent consumption (~20 g.L−1). An increased preparation temperature did not affect the Pb2+ adsorption at all, but it reduced the efficiency of AsO43− adsorption by up to 30%. The SK–FA composites proved to have promising properties, mostly as cation-active adsorbents.