Monday, November 13, 2006
127-18
Utilization of Zeolite for Reducing Sodium and Salt Concentrations in Saline-Sodic Coalbed Natural Gas Waters.
Girisha Ganjegunte1, George Vance2, Robert Gregory3, and Ronald Surdam3. (1) Texas A&M Univ System, 1380 A&M Circle, El Paso, TX 79912, (2) Univ of Wyoming, Dept of Renewable Resources, Laramie, WY 82071, (3) Wyoming State Geological Survey, P.O. Box 1347, Laramie, WY 82071
Coalbed natural gas (CBNG) production involves pumping water (e.g., CBNG water) from coal seams to reduce hydrostatic pressure in order to allow gas release. Unfortunately, CBNG water is dominated by sodium (Na+) and bicarbonate (HCO3-) ions, with sodium adsorption ratios (SAR) that can exceed generally acceptable levels for surface application. Therefore, management of CBNG water is a major environmental challenge because of its quantity and quality. We evaluated the use of a Ca-rich natural zeolites (80-90% clinoptilolite with a cation exchange capacity (CEC) of ~110 meq/g) for removing Na+, reducing SARs and enhancing the beneficial use of the treated waters. A column study was performed using two CBNG waters with different SARs (19 and 107 mmol½ L-½) and four zeolite size fractions. Results indicated initial leachate SARs of both CBNG waters decreased to <1.0 mmol½ L-½ after passing through zeolite columns. Exchange reactions involving high Na+ conditions suggested 1 tonne of zeolite, depending upon its size, can be used to treat 50,000 to 85,000 L of CBNG water to reduce SAR from 34 (typical in the Powder River Basin (PRB)) to an acceptable level of 10. The use of zeolite technology appears to be an efficient, effective and possibly affordable water treatment alternative that can maximize the beneficial use of CBNG water. The results of this laboratory study are being used to design an economically viable and efficient water treatment process for CBNG waters in the PRB of Wyoming and Montana .