Feasibility of Using Natural Zeolites to Remove Sodium from Coal Bed Methane-Produced Water

Abstract

Coal bed methane (CBM) is naturally occurring methane, contained in coal seams saturated with water. In order to extract the CBM, large quantities of water must be pumped from the coal seams. CBM water, produced in some areas of New Mexico, contains low total dissolved solids, which can potentially be used for rangeland irrigation. The water, however, has a high sodium adsorption ratio, which can result in severe deterioration of soil permeability with repeated irrigation. The St. Cloud zeolites exhibit a low selectivity of Na+ over Ca2+ (Vanselow selectivity coefficients of 0.26 and usable Na+ exchange capacity of 0.1 meq∕g ) at the ionic strength of Na+ -laden CBM waters (0.035 M) . Nevertheless, given the availability and low cost of natural zeolites, ion exchange experiments were conducted using packed columns to estimate a treatment cost. The operation and maintenance cost of the zeolite system was estimated to be about $3 per barrel (one barrel =159 liters) compared with $0.75–$4∕bbl for deep well i...