Abstract---Adsorption of Ni(II) by Ca-and Na-saturated kaolinites was studied in equilibrating solutions with total Ni concentrations ranging from 118 to 946/xg/liter. Background electrolytes used in these :experiments were 0.005, 0,0l, 0.025, and 0.5 M Ca(NO3)~, 0.002 and 0.005 M CaSO4,0.0l and 0.1 M NaNO3, and 0.005 and 0.05 M Na2SO4. Ion speciation in equilibrium solutions was calculated by the computer program GEOCHEM. Computed Ni 2+ concentrations and activities at equilibrium were correlated with total Ni adsorbed by kaolinite. Increasing ionic strength resulted in decreasing Ni adsorption. Adsorption of Ni was greater from solutions when NO3 was the dominant anion. Based on adsorption data in SO4 medium, the standard free energy of adsorption of Ni 2* ion on kaolinite was computed to be -27 k J/mole.

Solid waste from the Tripoli Sewage Treatment Plant is being used for manuring various crops in Al-Hadba production project. To monitor concentrations of several heavy elements, essential and nonessential to plants that are potentially hazardous to animal and human healthy by entering food chain via soil-plant system, samples of solid waste were collected monthly (every four weeks) during the years 1980-1981. These samples were appropriately handled and analized for total -N, P, K, Ca, Mg, Na, Fe, Mn, Cu, Zn, Cd, Cr, Ni, Co, and Pb.The sludge samples were found to contain an average of 2.00-2.22-0.31% when expressed as a mixed fertilizer (N-P2O5-K2O) respectively. Concentrations of Zn, Pb, Ni, and Cd were greater than their critical levels of 1500, 550, 150, and 15 ppm in 54, 58, 8, and 29% of the samples respectively. The concentrations of Cu and Cr were less than their critical levels of 750 and 500 ppm in all samples respectively.