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Interaction of Monomeric Silicic Acid With Copper and Zinc and Chemical Changes of the Precipitates With Aging¹

ABSTRACT

Precipitates were formed by titrating dilute, acidic solutions of monomeric silicic acid [Si(OH)₄] and copper (Cu) or zinc (Zn) to various pH values. Those containing Cu formed above pH 6.0; those containing Zn formed above pH 7.0. Periodically, during 2 years of aging in their mother liquor, the liquid phase was sampled and analyzed and the Cu/Si or Zn/Si molar ratios of the precipitates calculated. The Cu/Si ratios of those containing Cu stabilized readily near 0.78 and were unaffected by pH. The Zn/Si ratios of the Zn-containing precipitates, however, changed as a result of Si enrichment from near 1.80 soon after their formation to near 0.80 after aging 2 years. The systems with the lowest pH changed first and most rapidly and became stabilized within 6 months; those above pH 8.0 changed more slowly.

The Zn-containing precipitates gave diffuse X-ray diffraction patterns indicative of a 2:1 layer silicate, whereas those containing Cu were amorphous.

¹ Contribution from the Western Region, Agricultural Research Service, U. S. Dep. of Agric.

² Soil Scientist, Snake River Conservation Research Center, Kimberly, ID 83341.

Received for publication October 22, 1977. Accepted for publication October 25, 1977.