Phosphate Recovery Using Amorphous Calcium Silicate Hydrates
Amorphous calcium silicate hydrates (A-CSHs) can be chemically synthesized using abundantly available, inexpensive materials such as siliceous shale and calcium hydroxide. A-CSHs can serve as a bifunctional adsorption-aggregation agent for phosphate (Pi) recovery from aqueous solution. A-CSHs can also be prepared by soaking recyclable calcium silicates such as concrete sludge and steelmaking slag in a dilute hydrochloric acid solution. Since A-CSHs show high Pi removability, settleability, and filterability, they have the potential to offer a simple, cost-effective option to the recovery of Pi from Pi-rich waste streams. On-site experiments using a mobile, pilot-scale plant have showed that A-CSHs can recover approximately 80% Pi from a Pi-rich sidestream in a wastewater treatment plant. This chapter describes a simple process for Pi recovery from aqueous solution using A-CSHs as a bifunctional adsorption-aggregation agent.