Saturated permeability behavior of biochar-amended clay

Purpose Biochar has the characteristics of loose porosity, high specific surface area, and strong adsorption properties. Recently, the compacted biochar amended clay has been proposed as a sustainable alternative material for the final cover of landfills. However, the effect of biochar on saturated hydraulic conductivity (k(sat)) is not yet conclusive. The objective of this study was to determine the influence of biochar content on the permeability of biochar-clay mixed soils. Materials and methods The clay used in the study belongs to the low liquid limit clay. The biochar is produced by heating the rice straw under an oxygen-deficient condition at a temperature of 500 degrees C. To study the effect of biochar content on the permeability of biochar-clay mixed soils, the biochar-clay mixed soils with the mass percentage of biochar being 0%, 5%, 10%, 15%, and 20% were used. The saturated hydraulic conductivity of the biochar-clay mixed soils was measured by the head pressure control permeameter. Meanwhile, the micro-pore structure of the saturated biochar-clay mixed soils was obtained by the nuclear magnetic resonance (NMR) technique. Results and discussion It can be observed that the saturated hydraulic conductivityk(sat)of biochar-clay mixed soils increases linearly as the biochar content increases. The NMR results show that theT(2)distribution curve of pure clay is a unimodal pattern, while theT(2)distribution curve of biochar-clay mixed soils presents the bimodal pattern, whereT(2)is the transverse relaxation time, reflecting the pore size of the soil specimens. With the increase of biochar content, theT(2)spectrum of the mixed soils moves slightly to the right, andT(2)at main peak increases gradually, correspondingly the most probable pore size of biochar-clay mixed soils increases. Conclusions The pore size distribution of the soil was changed by the addition of biochar and subsequently affects the permeability of biochar-clay mixed soils. This study provides some useful suggestions for optimizing the pore structure of the biochar amended clay anti-seepage layer in the final cover of landfills.