Adsorption of Lead (II) Ions by Organosilicate Nanoporous Materials

Abstract

ADSORPTION OF LEAD (II) IONS BY ORGANOSILICATE NANOPOROUS MATERIALS Larry Keith Isaacs Old Dominion University, 2007 Director: Dr. Mujde Erten-Unal As-synthesized organosilicate nanoporous (OSNP) materials HMS (hexagonal mesoporous structure) and MCM-41 were used as adsorbents for removal of lead (II) ions in laboratory batch and column studies. Mesoporous organosilicates were prepared from tetraethylorthosilicate (TEOS) and either an ionic (cetyltrimethyl-ammonium) or neutral (dodecylamine) surfactant. Batch reaction distribution coefficients for MCM-41 were Kd = 51.5 L/g (SD 26.3) at 24 h and KD = 73.7 L/g (SD = 40.5) at 7 d. OSNP lead (II) ion adsorption increased from pH = 3 until pH ca. 7.5 after which a sharp decrease in adsorption was noted. OSNP materials reflected a dependence on ionic strength consistent with an outer-sphere complexation and electrostatic bonding mechanism. Lead (II) ion adsorption behavior in seven matrix batch solutions was not effective possibly due to soluble complexes that were formed that prevented adsorption and precipitation. There was no difference in the batch adsorption performance of MCM-41 and HMS. Column designs were optimized by response surface methods. OSNP material/sand media head loss at a superficial velocity = 0.49 m/h increased 28.1% compared with sand only media. At column break through, defined as Ce/Co = 0.5, MCM-41/sand media Kd = 46.2 L/g and sand only Kd = 0.04 L/g. There was significant evidence to warrant rejection of the claim that the variances in Kd were equal (P < 0.001, n = 12). Adsorption capacity in columns with synthetic adsorbates at Ce/Co = 0.50 were HMS = 0.013 mmol/g (2.74 mg/g) at 0.6 m3/m2 h and MCM-41 = 0.071 mmol/g (14.63 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. mg/g) at 2.1 m3/m2 h. For a stormwater treated by single pass column filtration, MCM41 lead (II) ion adsorption at Ce/Co = 0.50 was 0.028 mmol/g (5.88 mg/g) and sand only = 2.83E-05 mmol/g (0.01 mg/g). Water molecule ionization by metal cations decreased influent pH, combined with deprotonation of MCM-41 during adsorption of lead (II) ions, caused a decrease in pH sufficient to change column adsorption performance. The declining rate sand filtration cost for a 100 m2 unit in 2007 dollars was estimated at $31,600, however this did not include the cost for MCM-41 adsorbent materials, which are not available commercially. Adsorbent life cycle was calculated at 2.6 years. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Copyright, 2007, by Larry Keith Isaacs, All Rights Reserved. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. This dissertation is dedicated to my wife Marsha who has been forever patient and to our children for their constant encouragement. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.