The effect of zeolite treatment by acids on sodium adsorption ratio of coal seam gas water

Many coal seam gas (CSG) waters contain a sodium ion concentration which is too high relative to calcium and magnesium ions for environment acceptance. Natural zeolites can be used as a cheap and effective method to control sodium adsorption ratio (SAR, which is a measure of the relative preponderance of sodium to calcium and magnesium) due to its high cation exchange capacity. In this study, a natural zeolite from Queensland was examined for its potential to treat CSG water to remove sodium ions to lower SAR and reduce the pH value. The results demonstrate that acid activated zeolite at 30%wt solid ratio can reduce the sodium content from 563.0 to 182.7 ppm; the pH from 8.74 to 6.95; and SAR from 70.3 to 18.5. Based on the results of the batch experiments, the sodium adsorption capacity of the acid-treated zeolite is three times greater than that of the untreated zeolite. Both the untreated and acid-treated zeolite samples were characterized using zeta potential, surface characterization, DTA/TG and particle size distribution in order to explain their adsorption behaviours.

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► Coal seam gas waters contain high sodium concentration harmful to the environment.
► Natural zeolites are cheap for controlling Na adsorption ratio (SAR) of the water.
► Acid treated zeolite can reduce SAR to level below 20, accepted by authorities.
► SAR of the treated zeolite is 3 times lower than that of the untreated zeolite.
► Acid treatment improves the sodium adsorption capacity of CSG water.