The effect of the physical structure of a porous Ca-based sorbent on its phosphorus removal capacity

A macroporous calcium-based sorbent made from bentonite, calcium hydroxide and Yalloun coal was prepared and tested for its phosphorus removal performance. The coal was added as a solid pore-forming agent. Pores sizes as large as a few micron were generated when the Yalloun coal was incorporated at a relatively high proportion. These pores were formed due to the burning out of the added coal during the thermal treatment conducted at 700 degrees C. Results of phosphorus removal experiments showed that the increase of the amount of phosphorus removed could be positively correlated with the increase of the total pore volume and the mean pore size. Decreases in pore sizes and total pore volume were pronounced in sorbents used to remove phosphorus due to the formation of a Ca-phosphate mineral on their surfaces. It was suggested that the widely formed pores avoided the rapid plugging and contributed to maintain the diffusional transport of the substrate to a certain extent. Hydroxyapatite was formed and coated on the surface of the sorbent during phosphorus removal. On the basis of these results, it was concluded that modification of the physical structure of Ca-based sorbents by creating large pore sizes, revealed to be effective for increasing their phosphorus uptake.