Cd(II) and Zn(II) adsorption on lignite-derived humic substances and cattle manure biochar

Excessive industrial release of trace elements may pose a great risk to the environment. Conventional remediation treatments have considerable limitations, making less expensive new technologies an important research area. Batch experiments were conducted at room temperature to investigate the use of two lignite-derived humic products (nano-humus and humic powder) and a cattle manure biochar as adsorbents in the removal of cadmium and zinc from laboratory synthesized water. Nano-humus was most effective in adsorbing Cd(II), wherein 89% adsorption was rapidly achieved in 15 min. The adsorbed amount of Cd(II) and Zn(II) both increased with initial metal ion concentrations from 25 to 125 mg L⁻¹. Despite being produced from the same sources, nano-humus and humic powder showed different properties and adsorption behaviors. The adsorption mechanism of nano-humus followed the Freundlich isotherm model and pseudo-second-order kinetic model, indicating multilayer chemisorption. Humic powder followed the pseudo-second-order kinetic model, although it had a low isotherm model fit, implying chemisorption-dominated adsorption. Cattle manure biochar followed the Freundlich isotherm and pseudo-first-order kinetics model, suggesting diffusion-dominated multilayer adsorption. Of the three adsorbents tested, nano-humus had greatest potential as an effective and inexpensive material for metal remediation.