SOLID PHASE FORMATION AND SOLUTION CHEMISTRY OF NICKEL IN SOILS

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Abstract
Thermodynamic stability models of various nickel minerals and solution species are simulated to picture the possible solid phase formation and solution chemistry of Ni in soils. Carbonate, phosphate, sulfates, and halides of Ni are too soluble to precipitate in soils. Nickel oxides and hydroxides are stable in soils with pH greater than 9. The sulfides of Ni may control the concentration of Ni in soil solution if the soil environment reduces below pe+pH of 5. Nickel ferrite (NiFe2O4) seems the most probable solid phase that can precipitate in soils. Nickel phosphate (Ni3PO4)2 is comparatively more soluble than nickel ferrite and will probably form only in soils where the availability of Fe is limited. Nickel silicate and nickel aluminate (NiAl2O4) are also metastable with respect to nickel ferrite. Hydroxy-complex Ni(OH)+ and Ni2+ constitute a major portion of total Ni in soil solution above pH 8. In acid soils Ni2+, NiSO40, and NiHPO40 are significant and depend upon the levels of SO42- and PO43-. Bromo-, chloro-, iodo-, and nitrocomplexes of Ni are of minor importance in soils. © Williams & Wilkins 1984. All Rights Reserved.

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