Desalination of Irrigation Water Using Metal Polymers

Rain-fed and irrigated agriculture associated with salinized soil and saline water supplies is characterized by low crop yields. Partial desalination of this saline water will increase crop yields. Recent studies have established that supported metal polymers can be used to produce partially desalinated irrigation water without producing a waste reject brine. This study assesses the ability of more than 90 different unsupported metal polymer formulations (containing one or more of Al, Ca, Fe, K, Mg, Mn, and Zn) to remove Na+ ions and Cl− ions from saline water (seawater, brine, brackish water, and flowback water). The polymers were constructed using a simple sol-gel approach at ambient temperatures. The overall ion removal followed a first-order reaction. Removal selectivity between Na+ and Cl− ions was a function of polymer formulation. Mg@Al polymers preferentially remove Cl− ions, while Fe@Ca polymers tend to remove Cl− and Na+ ions in more equal proportions. Ion removal can be rapid, with >50% removed within 1 h. These results were used to develop a process methodology, which will allow most seawater, brackish water, and saline flowback water to be desalinated to form usable irrigation water.