COPRECIPITATION OF TRACE AND MINOR ELEMENTS IN MODERN AUTHIGENIC HALITES FROM THE HYPERSALINE DEAD-SEA BRINE

Modern halite samples were collected from the Dead Sea (post 1983) and analyzed for their minor (Br, Mn, K, Ca) and trace (Cd, Pb, Zn, Ni) e lement concentrations. The halites collected include sedimentary halit es with different morphologies and halites which crystallized on ropes suspended in the water body (rope-halites). The mechanisms of minor a nd trace element coprecipitation with these halites are discussed, and their apparent distribution coefficients are calculated (D-Mn = 0.09, D-K = 3.6 x 10(-4), D-Ca = 5 x 10(-5) D-Br = 0.011, D-Cd = 9.3, D-Pb = 3.5, D-Zn = 0.041, D-Ni = 0.11) mainly based on the sedimentary hali tes, which represent the slowest crystallization rates and are therefo re crystallized at or closest to equilibrium with the brine. Several t ypes of halites which crystallized at different crystallization rates exhibit large variations in coprecipitated Mn and to a lesser degree o f coprecipitated K and Ca. The wide range of calculated D-Br and D-K v alues in halites precipitated from the Dead Sea brine and from evapora ted seawater are probably due to kinetic factors and not to difference s in the parent brine compositions. The present study apparent distrib ution coefficient values probably best represent, both the Dead Sea br ine and evaporated seawater at similar ionic strengths. The continuous precipitation of halite since 1983 played a major role in the removal of Cd and Pb from the Dead Sea brine and only a minor role in the rem oval of Zn and Ni. Based on estimates of inventories in the Dead Sea, the removal flux of Cd and Pb are discussed. Copyright (C) 1998 Elsevi er Science Ltd.