Effect of temperature on the nickel humic acid equilibrium reaction

After disposal in underground repositories radionuclides may eventually come into contact with groundwaters containing humic acids at elevated temperatures. To study typical effects the Ni humic acid equilibrium reaction was investigated at 4°C, 20°C, 40°C, 60°C and 80°C. Experiments were conducted at pH = 4.5 and 6.5. Column and batch ion exchange techniques were used to compare labile and non-labile Ni HA binding levels. Overall the results indicated that Ni humic acid binding decreases with increasing temperature. Also at the higher temperatures some coagulation of the colloidal Ni humate occurs. Accordingly it is clear that the two phenomena, of decreased metal binding and coagulation, should in general reduce the possibility of enhanced metal mobility due to metal humate formation, at higher temperatures.