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In the 21st century, the problem of energy and environmental conditions become more serious. The food crisis is one of the big problems that should be solved. Securing the agricultural water is one of the most important factors in the food production. However, the region with the shortage of agricultural water is increasing according to the environmental problems such as desertification and the global warming. One of the ways to supply for water resource is seawater desalination. In desalination technologies, multi-stage flash (MSF) or reverse osmosis membrane method (RO), is famous all around the world [1]. In these desalination technologies, almost ions contained in seawater are removed, and make the fresh water high quality for domestic or industry. However, the water made by MSF or RO is expensive for agriculture. Seawater contains the essential elements needed for plant growth, but its high concentration of NaCl causes salt damage that precludes its direct use. Therefore, it would be possible to produce the irrigation water from seawater by reducing the NaCl using a simple-process. In an earlier study, we suggested a simple method to reduce NaCl concentrations in seawater using calcined hydrotalcite-like compounds and natural zeolite; radish sprouts were grown in the resulting solution [2-5]. This method is two-step process using a calcined hydrotalcite-like compound (CHT) in 1st-step and a natural zeolite in 2nd-step. In the 1-st step, Cl in seawater could be reduced by CHT to produce anion-reduced solution with high pH, which cannot cultivate plants, and then in the 2nd-step, treatment of natural zeolite can reduce Na content and can neutralize pH of the solution, simultaneously, to produce the solution with the ability to grow radish sprout. Therefore, this process has possibility to supply the water to irrigation. PO4 and NO3 ions were the nutrients for crops, but these concentrations in seawater are minor. The average concentrations of PO4 3and NO3 in seawater are 62 μg/L and 420 μg/L, respectively [6]. As for the water used as agricultural water, it is desirable for the crop to contain these elements for cultivation. It would be possible to produce the solution with PO4 3and NO3 by the improved procedure that the anion-reduced solution was neutralized with phosphoric or nitric acids, and then treated with natural zeolite to reduce Na content. This has advantage for the supply of nutrients to the cultivation solution. However, little information can be available on the effect of phosphoric and nitric acids on the ion exchange with natural zeolite in anion-reduced solution. In this study, the pH of the anion-reduced solution with phosphoric and nitric acids was neutralized, and the effect of phosphoric and nitric acids on the ion exchange with natural zeolite was investigated.

international journal of the society of materials engineering for resources

Effect of HNO&lt;sub&gt;3&lt;/sub&gt; and H&lt;sub&gt;3&lt;/sub&gt;PO&lt;sub&gt;4&lt;/sub&gt; on Ion Exchange of Natural Zeolite for Making Agricultural Cultivation Solution from Seawater