Phosphorus sorption capacity of different types of opoka

The bedrock opoka has been lately reported as an appropriate reactive media for onsite wastewater treatment systems due to its high phosphorus (P) sorption capacity. However, variations on its chemical composition may affect its reactivity with P, therefore leading to a variable P removal efficiency. In this paper, the P-sorption capacity of three different types of opoka from the region of Miechów, Poland, is reported. According to the silica and carbonate content, opoka samples were classified as light-weight and heavy-weight opoka. When heated over 900°C, opoka showed a very high P-sorption capacity that was well correlated to its Ca content. P-sorption isotherms from batch experiments with an artificial P solution were plotted and fitted to the Langmuir and Freundlich adsorption models. The Freundlich isotherm appeared to model better the P-sorption of light opoka and the Langmuir isotherm of heavy opoka, suggesting different dominating mechanisms of P-sorption by light and heavy opoka.