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Reactions of Phosphate with Soluble and Exchangeable Nickel^{1, 2,}

ABSTRACT

When solutions of NiCl₂ and KH₂PO₄ were titrated with NaOH, the immediate reaction product was an amorphous precipitate having a composition corresponding to 6NiHPO₄ · Ni(OH)₂ · 7H₂O or 4NiHPO₄ · Ni₃(PO₄)₂ · 9H₂O. At all pH values < 7, the precipitate was free of Ni(OH)₂ or had a constant Ni(OH)₂ content, but at pH values > 7, the Ni(OH)₂ increased with increase in pH. When the amorphous precipitate was incubated at 25°C., crystalline products began to appear at 4 weeks and at 12 weeks the crystallization appeared to be complete. The main crystalline product was Ni₃(PO₄)₂ · 8H₂O. Crystallization was accompanied by acidification and also by a large reduction in the solubility of Ni. In the pH range of 6.5 to 7 the solubility of Ni was reduced to about 2 ppm.

Nickel-saturated clays treated with phosphate showed the same reactions as found in solution. The exchangeable Ni was reduced to about 3% saturation.

¹ Paper No. 1508, Univ. of California Citrus Research Center and Agri. Exp. Sta., Riverside.

² Support of this work by a grant (G18857) from the National Science Foundation is gratefully acknowledged.

³ Associate Professor, Laboratory Technician and Graduate Student, respectively, of the Dept. of Soils and Plant Nutrition.

Received for publication October 7, 1963. Accepted for publication December 27, 1963.