TRANSFORMATION OF SULFUR 



607 



Elementary sulfur is oxidized to sulfuric acid: 



2S + 30 2 + 2H 2 = 2H 2 SO« 



The sulfur is oxidized quantitatively without any intermediary reactions taking 

 place (table 63). 



In the presence of. tricalcium phosphate, the sulfuric acid interacts giving 

 first di-calcium phosphate, then mono-calcium phosphate and finally phosphoric 

 acid (figs. 43, 44): 



Ca 3 (P0 4 ) 2 + H 2 S0 4 + 2H 2 = Ca 2 (HP0 4 ) 2 + CaS0 4 -2H 2 

 Ca 2 (HP0 4 ) 2 + H 2 S0 4 + 2H 2 = Ca(H 2 P0 4 ) 2 + CaS0 4 -2H 2 

 Ca(H 2 P0 4 ) 2 + H 2 S0 4 + 2H 2 = 2H 3 P0 4 + CaSO«-2H,0 



1CK00 

 9600 





SQj. in MG 



P 2 5 in MG 



5 10 15 20 25 30 

 PERIOD OF INCUBATION IN WEEKS 



Fig. 43. Course of accumulation of citrate-soluble P 2 O s and S0 4 in composts 

 of soil-rock phosphate and sulfur (from Lipman, McLean and Lint). 



When the sulfur is oxidized by the denitrifying organism, the reaction may 

 take place as follows: 



5S + 6KN0 3 + 2CaC0 3 = 3K,S0 4 + 2CaS0 4 + 2C0 2 + 3N 2 



5Na 2 S 2 3 + 8KNO3 + 2NaHC0 3 = 6Na,S0 4 + 4K 2 S0 4 + 2C0 2 + 4N 2 + H 2 



