Use of zeolites for treating natural gas co-produced waters in Wyoming, USA
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Fast development of the coalbed natural gas (CBNG) industry in many parts of the western US has resulted in the co-production of potentially saline-sodic waters, hereafter referred to as CBNG water. Management of CBNG water is a major environmental challenge because of its quantity and quality. In this study, the potential utilization of three calcium (Ca2+)-rich zeolites were examined for removal of sodium (Na+) from CBNG waters. The zeolite samples examined were from the St. Cloud (ST) mine in Winston, NM, the Bear River (BR) mine in Preston, ID, and a mine in Arizona (AZ). The zeolite materials were used in adsorption and column experiments to evaluate sorption as a function of water chemistry, particle size and flow rate. Regeneration and potential reuse of the media were also examined. Surrogate CBNG waters that simulated the water chemistry of CBNG waters were used in the different studies. Although the AZ-zeolite is a Ca2+-rich chabazite, results from column studies indicate there was essentially no Na+ exchange, suggesting the Ca2+ is tightly held on chabazite adsorption sites. Results for ST-zeolite and BR-zeolite, which are clinoptilolite zeolites, indicated that a Langmuir model fit the adsorption data well. The maximum adsorption capacities from the adsorption curves for ST-zeolite and BR-zeolite were 9.6 and 12.3 (mg/g), respectively, accounting for approximately 38% and 39% of their measured CEC values. Column studies indicated that a metric tonne (1,000 kg) of ST-zeolite and BR-zeolite can be used to accumulatively treat 16,000 and 60,000 L of CBNG water, respectively, in order to lower the sodium adsorption ratio (SAR, mmol1/2L-1/2) of the simulated CBNG water from 30 to an acceptable level of 10. Based on the results of this study, Na+ removal with clinoptilolite zeolite appears to be a potential water treatment technology for maximizing the beneficial use of poor-quality CBNG water. Ongoing studies are evaluating water treatment techniques involving the direct application of zeolite to CBNG waters and development of a field scale prototype. 2008.