Evaluation of two organoclays, clinoptilolite, and hydroxy-apatite as sorbents for heavy metal removal from water

A series of column tests were performed with four sorbent media to determine their effectiveness for the removal of heavy metals from water. The sorbents are an organoclay, an organoclay/anthracite blend, clinoptilolite (a zeolite), and hydroxy-apatite. Heavy metals studied were Ni, Cr, Cu, Cd, and Zn. Four column tests were conducted using an influent solution containing all four metals (one test for each sorbent). Four column tests were conducted using an influent solution containing only Zn (on a for each sorbent), and two column tests were conducted using an influent solution containing only Ni (with clinoptilolite and hydroxy-apatite only). For the Zn-hydroxy-apatite experiment, the inflow solution also contained 200 mg/L Ca++ to simulate hard water. Aside from ion-selective resins, hydroxyapatite is the only sorbent that is believed to retain its sorption capacity for metals in hard water. Metal effluent breakthrough data indicated that the organoclay and the organoclay/anthracite blend removed all heavy metals, but only to a limited extent, with effluent metal concentrations equal to 50% of the influent concentration appearing after 2 to 3 pore volumes of flow. These sorbents have the unique capability of removing both hea vy metals and nonpolar organic pollutants from water simultaneously. Hydroxy-apatite demonstrated the greatest removal of metals from solution. Pore volumes of flow required to produce effluent concentrations equal to 50% of the influent concentration r anged between 50 (Ni) and 160 (Cu). Although hydroxy-apatite performed best for metal removal, it should be noted that clinoptilolite is superior to most media for ammonia removal.