Fractal analysis and pore structure of gasification fine slag and its flotation residual carbon

Abstract

Gasification fine slag is a kind of solid waste, and there is a large number of fine slags need to be recycled and reused for environmental consideration. The froth flotation kinetics experiment was adopted to recycle the residual carbon, carbon recovery percentage of 52.65% and the loss on ignition (LOI) of 64.47% were obtained. The pore structure and fractal characteristics of fine slag and its flotation residual carbon are essential factors which will influence their physical and chemical properties, including mechanical, adsorption and fuel properties and it is imperative to understand these parameters. In this study, BET, HK, BJH and FHH models of low-temperature N2 adsorption/desorption were used to compare the differences of specific surface area, pore size/volume and fractal characteristics among samples, respectively. As a result, there are larger surface area and fractal dimension value (D), smaller pore volume and average pore diameter of fine slag than that of flotation residual carbon, which is caused by the spherical-ash particles covering the surface and pores of the rough carbon matrix. Comparing the fine slag and flotation residual carbon, surface area decreases from 145 to 111 m2/g, pore volume increases from 0.1288 to 0.1833 cm3/g, and average pore width increases from 5.2141 to 6.0436 nm. Moreover, the values of D2 and D1 decreased by 6.77% and 2.89%, correspondingly. From the perspective of energy utilization, the HHV value of gasification fine slag is elevated from 6.22 to 19.48 MJ/kg after flotation kinetics process and LOI value increases from 24.49 to 64.47% respectively. TGA shows that the flotation residual carbon has better reactivity than raw fine slag. Froth flotation is an efficient approach to recycle residual carbon from fine slag, while the low-temperature N2 adsorption/desorption technology can be innovatively applied to characterize the pore structure and fractal characteristics of gasified fine slag.