Effect of HNO3 and H3PO4 on ion exchange of natural zeolite for making agricultural cultivation solution from seawater

Abstract

Effects of HNO3 and H3PO4 on ion exchange of natural zeolite in a new-simple process, which is a twostep process using calcined hydrotalcite and natural zeolite, for making agricultural cultivation solution were examined. The anion-reduced solution obtained by the treatment of seawater with calcined hydrotalcite (CHT-solution) was neutralized with phosphoric (CHT-solution-H3PO4) or nitric acids (CHT-solution-HNO3), and each four solutions (seawater, CHT-solution, CHT-solution-H3PO4 and CHT-solution-HNO3) was treated with natural zeolite to compare the ion exchange behaviors among these solutions. The pH of the all solutions can be neutralized to 5.5 by zeolite treatment, and the Na+ content can be removed from the all solution. The tendencies of Na+ removal in all solutions are almost same, and percentages of Na+ removal from all solutions are above 95% over 8 times zeolite treatment. The amounts of supplies for K+, Mg2+ and Ca2+ to the CHT-solution-HNO3 is higher than those of other solutions up to 6 times treatment. While almost PO43- was removed, NO3- was remained in the solution, over 6 times treatment with natural zeolite. Therefore, NO3- is possible to be supplied to the solution as nutrient in the two-step process, but PO43- isn't possible.