Properties of sludge generated by the treatment of fluoride-containing wastewater with dicalcium phosphate dihydrate

Abstract

Fluoride-containing wastewater is discharged from various industrial sites, including semiconductor, plating, and metal-treatment plants. To remove the fluoride, we treated wastewater with dicalcium phosphate dihydrate (DCPD, CaHPO 4 Á2H 2 O) to form fluorapatite [Ca 10 (PO 4 ) 6 F 2 ] crystals. We investigated the fluoride removal efficiency and the properties of the resulting sludge. For comparison, we also treated wastewater using conventional aluminum coprecipitation. The DCPD used in this study was a by-product of the gelatin industry. Nanoscale precursor particles were induced on the DCPD by treatment with warm water. After treatment of fluoridecontaining wastewater in batch experiments, the amount, particle size distribution, settleability, and filterability of the resulting sludge were measured to assess the usability of DCPD. We found that the amount of chemical additives required for the DCPD method was less than that for the conventional method. Additionally, the amount of sludge produced using the DCPD method was small and the final fluoride concentration was below 5 mg L -1 . In settleability tests, the sludge produced by the DCPD method was precipitated within 10 min. In filterability tests, most DCPD sludge was separated within 5 min. The settleability and filterability of sludge from the DCPD method were better than those of the conventional method. The release of fluoride from the DCPD sludge was below the levels stipulated by Japanese soil pollution regulations. Consequently, the sludge was considered unlikely to cause soil pollution, thereby facilitating landfill management. We concluded that DCPD can be used effectively to treat fluoride-containing wastewater and that the resulting sludge is unlikely to cause environmental damage.

Reactivity Improvement of Dicalcium Phosphate Dihydrate with Fluoride for Its Removal from Waste and Drinking Water

“…Further, FAp formed from the HAp-coated DCPD maintained initial DCPD shapes [9] as the same as that formed from the DCPD as in our previous study [7], while that from the HAp-mixed DCPD has quite smaller size than that from the DCPD [9]. Particle size of FAp formed from the DCPD is not change significantly from it of initial DCPD [14]. These difference came from crystals for template of FAp formation.…”

Enhanced reactivity of dicalcium phosphate dihydrate with fluoride ions by coating with apatite nanoparticles

“…Moreover, the addition of flocculants is not required, leading to a decrease in the sludge volume. Therefore, the use of DCPD is beneficial to water treatment because of the elimination of the need for chemical additives, the reduction in the amount of sludge, and the lowering of operational costs [16].…”

Improving the properties of dicalcium phosphate dihydrate (DCPD) powder by changing the morphology

“…Such problems associated with formation of the precursor can be solved by induction of a nano-scaled precursor on DCPD particles as an effective pretreatment method; this enhances the chemical reactivity such that it approaches the theoretical efficiency and proceeds with low concentrations of fluoride ions. 12), 13) This pretreatment prepares DCPD by providing it with the appropriate qualities and the ability to perform fluoride ion immobilization more effectively than existing competing methods, 14) such as methods using aluminum sulfate, 15) physical adsorption with carbonized bone (bone char), 16) and application of various adsorbents. 17) On the other hand, no studies have investigated the powder properties of DCPD particles.…”