The screening of various biochars for Cd2+removal at relevant soil pH

Abstract

Fourteen biochars from seven biomass sources were investigated on their long-term Cd2+ removal. The experiments consisted of a ten-day batch Cd2+ adsorption in a pH-buffered solution (pH = 6) to minimise pH effects. Insect frass, spent peat and chicken manure-derived biochars are promising Cd2+ adsorbents. Pyrolysis temperature was crucial for optimising Cd2+ removal by insect frass and spent peat-derived biochars. For these biochars, a pyrolysis temperature of 450 degrees C was optimal. In contrast, the Cd2+ removal by chicken manure biochars was independent of pyrolysis temperature. The Cd2+ removal by insect-frass and spent peat-derived biochars was associated with chemisorption on surface functionalities, while using chicken manure biochars was more associated with Cd2+ precipitation. The kinetics of Cd2+ removal over the course of ten days showed that insect frass biochar (450 degrees C) showed a gradual increase from 36 to 75 % Cd2+ removal, while chicken manure and spent peat-derived biochar (450 degrees C) already showed a higher Cd2+ removal (72 - 89 %) after day 1. This evidences that a long-term Cd2+ removal effect can be expected for some biochars. This should certainly be taken into consideration in future soil-based experiments.