Utilization of coal fly and bottom ash pellet for phosphorus adsorption: Sustainable management and evaluation

Recycling of coal combustion solids can have several environmental benefits. The objective of this study was to evaluate a sustainable approach to recycle coal fly ash and bottom ash as pelletized-adsorbents for dissolved phosphorus (P). Sodium Dodecyl Sulfate (SDS), a foaming agent, was added to enhance the phosphorus adsorption capacity of fly ash pellets (FAP) and bottom ash pellets (BAP) during the pellet fabrication. Ten types of fly ash pellets and bottom ash pellets with varying Sodium Dodecyl Sulfate proportions (FAP-0/BAP-0: 0% SDS; FAP-1/BAP-1: 2% SDS; FAP-2/BAP-2: 4% SDS; FAP-3/BAP-3: 6% SDS; FAP-4/BAP-4: 8% SDS by weight) were manufactured with a high temperature (700℃) modification process. The results indicated that the bottom ash pellet was more suitable adsorbent than fly ash pellet due to the better phosphorus adsorption capacity and lower heavy metal leaching. After the addition of Sodium Dodecyl Sulfate, the volumetric porosity of fly ash pellets and bottom ash pellets increased by 45.5%–163.6%, 52.9%–76.5%, respectively. However, higher Sodium Dodecyl Sulfate fraction did not result in better pellet phosphorus removal, since FAP-2 and BAP-3 resulted in the highest phosphorus removal among the pellets tested in this study. The results from X-ray diffraction demonstrated that Calcium and Silica were the major phases in the pellets. This study provides a feasible approach to reuse fly ash and bottom ash as effective pelletized-adsorbents for water quality improvement. These pellets can be applied in edge-of-field and in-stream treatment to control P loss from the agricultural area.