Characteristics of foam sol clay for controlling coal dust

Abstract

A foam sol clay (FSC) mixture, mainly composed of fly ash (FA), surfactant (n-amylamine) and polyethylene oxide (PEO), was proposed for coal dust control. The FA surface, modified by a FSC solution, stability and foamability were investigated. It was found that the FA surface in alkaline solution was deprotonated to form a negative charge, which could be adsorbed by the polar head group of n-amylamine via electrostatic interactions. As a result, with increasing surfactant, the particles gradually converted from hydrophilic to hydrophobic and attached at gas-liquid interfaces so that the contact angle, zeta potential, froth stability and foamability increased. At a surfactant concentration (ca) of 35 g/L, a monolayer three-dimensional network was formed and the maximum foamability and half-life were obtained. Upon further increasing ca, a bilayer and particle clusters were formed by surfactant chain-chain interaction, resulting in particles becoming hydrophilic again, and the FSC solution having stronger mechanical resistance against flowing, so that the viscosity rapidly increased and the diffusion of free surfactant molecules was hindered at the froth surfaces. Thus, the contact angle, froth stability and foamability decreased. PEO could bond sodium dodecyl sulfate and water to form a dual adsorption layer and hydrogen, respectively, which enhanced the wettability of the FSC on coal dust surfaces. PEO could adsorb and curl FA particles to form a thin layer of armor after froth air-drying. It was concluded that the froth generated by the FSC solution, including 200 g/L FA, 35 g/L ca and 1 g/L PEO, could control coal dust with a long-term effect.