The Heterogeneous Reverse Osmosis Membranes Based Separation of Fluorides with Fly Ash Pretreatment

The objective of this paper was to examine the separation efficiency of fluorides by heterogeneous reverse osmosis membranes made from cellulose acetate and modified coal with aryl diazonium salt (batch 318 K) and lignite based fly ash pretreatment. The effect of varying the feed concentration (400-100 mg/dm³) of sodium and ammonium fluorides on performances of these membranes using 400 mg/dm³ aqueous solution of sodium chloride as referent system at 1.76 MPa have been investigated. Practically no significant change in the membrane characteristics (product rate, and solute separation) by varying the above concentration of feed salt solutions. The high separation of fluoride (synthetic sample) ≈99% was obtained by resulting membranes pretreated with different amount and contact time of low cost adsorbent (fly ash) at pH 4. A sample of waste water effluents of cement industry was also treated with above membranes without pretreatment and the results are presented. These data indicate that the fluoride ion concentration are within acceptable level as far as environmental limits concerned, therefore, their practical application produced water of suitable quality, essentially free from fluorides.