Biosorption (removing) of Cd(II), Cu(II) and methylene blue using biochar produced by different pyrolysis conditions of beech and spruce sawdust

Abstract

The influence of pyrolysis parameters (temperature, heating rate) on adsorption properties of wood charcoals was studied. Beech and spruce waste sawdust were investigated by TG–MS technique, and it was revealed that pyrolysis of sawdust consists at least of two overlapping reactions characterized by different values of activation energy E a (151 and 184 kJ/mol for beech sawdust, 157 and 172 kJ/mol for spruce sawdust). Based on obtained results, adsorbents from studied sawdust were prepared through pyrolysis at 400–700 °C with heating rate 10 or 2 K/min and their surface and adsorption characteristics were investigated. It was found that higher pyrolysis temperature (700 °C) and higher heating rate (10 K/min) generally improved micropore surface areas of beech and spruce biochars. The adsorption capacity of spruce biochar for Cu(II) and Cd(II) increased with higher pyrolysis temperature and lower heating rate (2 K/min) up to 0.14 and 0.12 mmol/g, respectively. In the case of beech biochar, the adsorption capacity for heavy metal ions has no distinct dependence on pyrolysis temperature nor heating rate. The opposite effect of heating rate was found in the case of the methylene blue uptake, better adsorbent can be prepared by pyrolysis with heating rate 10 K/min. The effect of pyrolysis temperature is not clear in this case.