Application of XRD to the mineralogy of the salt-efflorescences on the salt-affected soils of Punjab, Pakistan

Being most powerful XRD was chosen for mineralogical investigation of the salt effloresence. A total of 12 salt crusts (winter 1990-91), were collected from the Rechna Doab. Solution chemistry (1:10 salt : water) revealed percent contribution of anions [SO/sub 4/sup 2-/ +HCO/sub 3/ = 2.55 and Cl' 1.6%] and cations [Na+ = 96.9%, Ca/sup 2+/+ Mg/sup 2+/ = 2.7% and K+ = 0.4%]. This shows significant differences in values of (SO/sub 4/)/sup 2-/ and Cl' and rejects the hypothesis of Cl' dominance in these soils, now it seems to vanish in these areas. For XRDA only 6 salt efflorescences were selected, based on their similarity in solution chemistry. The XRD established that the mineralogy is dominated by thenardite (Na/sub 2/SO/sub 4/) in all. Other minerals in variable amounts were trona [Na/sub 6/Ca(SO/sub 4/)/sub 4/], Bloedite [Na/sub 4/Mg(SO/sub 4/)/sub 2/.4H/sub 2/O], Natron (Na/sub 2/CO/sub 3/.10H/sub 2/O), Halite (NaCl) and Calcite (CaCO/sub 3/). The analysis conforms closely to the expectations of dominance of minerals having Na+ and SO/sub 4/sup 2-/ in their crystal structure, guessed from the solution chemistry of these salt efflorescences. (author)