Synthesis of porous alkali-activated materials for high-acidic wastewater treatment

Abstract

Many industries and industrial processes, such as electroplating, acid mine drainage, the pharmaceutical industry, and industries that use phosphorous, produce large volumes of acidic wastewater that must be treated before discharge. Generally, a large quantity of an alkali, such as lime, caustic soda, or soda ash is used to neutralize the acidic wastewater and it is a costly treatment process. Therefore, new self-releasing alkali materials were studied. This research proposed the synthesis of sustainable porous alkali-activated materials (porous AAMs) by a simple method for acidic wastewater treatment. Industrial wastes, i.e., fly ash and bottom ash from a power plant, were employed to produce porous AAMs using sodium silicate solution as a foaming agent. The test results showed that fly ash and bottom ash AAMs had the potential to be used as pH modifiers. 0.001 M HCl solution (pH of 3) was selected as the representative acidic wastewater, and the pH of the solution fell to within the allowable discharge pH range of 5.5–9.0 according to the effluent discharge standard of Thailand. The retention time was three days for a solid-to-solution ratio of 1:500 w/v (g/ml). Porous AAMs present an attractive way of utilizing waste coal ashes compared to a cost-effective method for acidic wastewater treatment.