19 

 No specific inorganic mineral has been identified as a sink for 

 soluble sulfates in the well-drained, acid soils of the southeastern 

 United States. Adams and Rawaj f ih (1977) proposed that sulfate reten- 

 tion by acid soils may be a consequence of the solubility of basalumi- 



nite, Al. (OH) in SO. -5H.0, and/or alunite, (Na/K)A1_ (OH) , (SO, ) „ , as well 

 4 1U 4 z J 6 4 Z 



as adsorption reactions. Based on earlier work by Singh and Brydon 

 (1967, 1969), Adams and Rawajfih were able to show through precipita- 

 tion experiments and calculated soil solution ionic activities that 

 soil solution sulfate could be removed by precipitation as basaluminite 



and alunite. An increase in soil pH could be expected to be accom- 



2- 

 panied by an increase in solid-phase Al(OH)--.and solution SO, because 



of the following reactions: 



Al,(0H) in S0. + 20H~ ^ 4A1(0H), + SO ~ 



4 10 4 i 4 



KA1-(0H)_(S0, )„ + 30H~ ;p^3Al(0H) + K + + 2S0?" . 

 3 6 4 2 3 4 



These minerals have not been identified in soils, but Adams and 

 Hajek (1978) further demonstrated that formation of these compounds in 

 sulfate-containing acid soils was thermodynamically feasible. Precipi- 

 tation occurred with as little as 10 mM sulfate in the reacting 

 solution. 



Using basaluminite and alunite as sources of sulfate for cotton 

 seedlings ( Gossypium hirsutum L. ) grown in a greenhouse in a sandy loam 

 soil from a Typic Hapludult at a pH of 6.5, Wolt and Adams (1979) 

 demonstrated that S in basaluminite was more available while that in 

 alunite was almost unavailable. Their data supported the previous 

 thesis of Adams and Rawajfih that sulfate "adsorption" and "desorption" 

 in acid soils could be partially due to solubility behavior of Al and 

 Fe hydroxy-sulfates. 



