Prospective chemisorption of fluoride utilizing coastal molluscan (Crassostrea Sp.) shell from phosphatic fertilizer pond wastewater, Paradeep, Odisha

Abstract

The present study explores the utilization of very acidic (pH 1.46) and high fluoride (F-) containing (9290 ppm) phosphatic fertilizer industry (Paradeep, Odisha, India) pond wastewater (PW) generated from phosphogypsum (PG) stacks by using Crassostrea Sp. molluscan shell (MS) as an adsorbent. F- chemisorption batch experiments on molluscan shells (MS) powder (212 - 500 micron) varying 6 different MS (Solid-S) to PW (Liquid-L) i.e. S/L ratios (1: 8 to 1: 30), time (0.08 to 48 hours) and fluoride concentration (4645 – 8361 ppm) as diluted PW. Chemisorption of F- peaked with 1: 20 S/L ratio at 24 hrs and its concentration in the supernatant reduced by 99.9 %. XRF, FTIR and XRD analysis of MS and its chemisorbed residues confirmes the role of relatively high calcium containing MS (72 % CaO) towards formation of Fluorapatite (FA) [Ca5(PO4)3F]. Desorption experiments of FA residue for 24 hrs, highlights the stability of F- chemisorption process on MS, which is confirmed by presence of FA in desorbed residue through XRD analysis. The research findings establish prospects of F- recovery from PW through chemisorption process utilizing selected MS.