Nickel sorption and speciation in a marine environment

Six sediment samples were collected from the northern Arabian Gulf. Nickel was added to each sediment- seawater suspension and the concentration of total dissolved Ni in the suspensions was monitored for 75 days. The analytical data were used to obtain a linear regression equation relating Ni²⁺ activity in the sediment suspensions to pH. Using this equation and thermodynamic information, the distribution of Ni species in the suspensions was calculated. The major inorganic species, extrapolated to 35 salinity and pH 8.1, were: Ni²⁺ (60.1%), NiCl⁺ (16.9%), NiCl_inf2^sup0(5.0%), NiOH⁺ (0.4%), and NiSO_inf4^sup0(17.5%). An increase in the seawater salinity increased the concentration of total dissolved Ni and Ni chloro-complexes. A decrease in pH of seawater increased total dissolved Ni and decreased NiOH⁺ complex, but the proportion of other species remained unchanged. There was no significant (P < 0.05) effect of Cu, Cd, Pb, Fe, Mn, and Al additions on Ni sorption in the marine sediment suspensions.