Effect of humic acid on copper adsorption by Kaolin

Varying amounts of humic acid (Na-salt; 0 to 10 ppm) were first equilibrated with a dilute suspension of H⁺ -Kaolin and then with spiked (high activity radioactive ⁶⁴Cu) water. After filtration, through a 0.45 µm Millipore membrane, the amount of radioactivity on the filter and the filtrate was measured separately using a Gamma ray well counter. Adsorption of Cu (expressed as distribution coefficient — K _d ) was plotted against humic acid concentration. K _d values decreased sharply upto 1 ppm humic acid concentration and thereafter remained constant up to 10 ppm.