Basaluminite and Alunite: A Possible Cause of Sulfate Retention by Acid Soils

Abstract

Pure‐solution and soil‐solution experiments were conducted in which the solubility products of synthetic basaluminite and alunite in pure solutions were compared with the ion‐activity products of Al4(OH)10SO4 and KAl3(OH)6(SO4)2 in soil solutions of sulfate‐treated soil. Solution experiments were conducted in which 0.05M Al2(SO4)3 was titrated with NaOH, KOH, or Ca(OH)2 to an OH/AI mole ratio of 2.0. The initial precipitate was amorphous, with the chemical composition of basaluminite, Al4(OH)10SO4·5H2O. Aging the amorphous precipitates under different conditions transformed them to compounds of different composition and crystallinity: amorphous precipitate remained unchanged when aged in their mother solutions at 25°C; crystalline basaluminite formed in Ca mother solutions when aged at 50°C; crystalline alunite formed in Na and K mother solutions when aged at 50°C; crystalline alunite formed in K mother solutions that had been seeded with alunite or bentonite when aged at 25°C. The solubilities of the amorphous and crystalline precipitates were determined in dilute NaClO4 solutions and gave the following average calculated pKsp values: 116.0 for amorphous basaluminite; 117.7 for crystalline basaluminite; 79.7 for Na‐alunite; and 85.4 for K‐alunite. Similar Ksp values for basaluminite were found for soil solutions from a sandy loam soil that had been treated with different rates of K2SO4. However, the soil solutions were supersaturated with respect to alunite. When the SO4‐treated soil was subsequently treated with a high rate of KH2PO4, the soil solution remained supersaturated with respect to alunite, but became undersaturated with respect to basaluminite. It is proposed that sulfate retention by acid soils is a consequence of the solubility of basaluminite and/or alunite.

Gesso e calcário aumentam a produtividade e amenizam o efeito do déficit hídrico em milho e soja

“…A redução nos teores de Al 3+ tóxico, em decorrência da aplicação de gesso, ocorre pela precipitação de Al e formação de minerais (Adams & Rawayfih 1977), ou, também, pela lixiviação de Al com o gesso, na forma de pares iônicos ou complexos AlSO 4 + (Pavan et al 1984).…”

Metal-Induced Sulfate Adsorption by Soils

“…Barite (BaSOJ has been found in a variety of soils (Crum and Franzmeier, 1980;Lynn et al, 1971) and celestite (SrSO^) was identified in some arid soils (Abtahi et al, 1980 (Adams and Rawajfih, 1977;Carson and Dixon, 1983;Clark et al, 1961;Fleming and Alexander, 1961;Hue et al, 1985;Khanna et al, 1987;Nordstrom, 1982;Tsai and Hsu, 1984;Wagner et al, 1982;Wolt, 1981). In addition, other Na-rich Fe or A1 sulfates such as natrojarosite [NaFe3(0H)g(804)2] (Pawluk and Dudas, 1978) and natroalunite [NaAl3(0H)g(804)2] (Chitale and Guven, 1987) may form in some soils.…”

“…He also hypothesized that jurbanite may form from gibbsite and is responsible for activity in acid forest soils. Earlier studies by Adams and Rawajfih (1977) showed that Al-hydroxyl surface of the solid phase could be an important mechanism controlling 80/' and Al®" activities in soils. In their experiments, they showed that the formation of sparingly soluble alunite and basalunite from, or onto the surface of gibbsite, was thermodynamically favorable.…”

Doses de enxofre e tempo de incubação na dinâmica de formas de enxofre no solo

“…Numa superfície positiva, o SO 4 2-é adsorvido como bidentado, formando estrutura anelar de seis membros que, segundo Hingston et al (1974), favorece a irreversibilidade, ou seja, formas não lábeis. Adams & Rawajfih (1977) sugeriram a precipitação e dissolução da basalunita e alunita e de sais análogos de Fe como mecanismos plausíveis para os fenômenos de sorção de SO 4 2-em solos ácidos.…”