Adsorption of humic and fulvic acid on copper surfaces
The presence of natural organic matter (NOM) in drinking water can increase the levels of copper released from copper pipes to water and inhibit the formation of protective deposits such as malachite. Since adsorption of NOM on copper pipes surfaces is believed to be one of mechanisms that explains this phenomenom, the objective of this study was to determine kinetics and the adsorption equilibrium of main components of NOM, humic acid (HA) and fulvic acid (FA), onto copper surfaces. The kinetics and equilibrium adsorption of HA and FA on copper foils were examined using batch experiments at 22°C. HA and FA followed pseudo second-order kinetics adsorption. Rate constants measured were 2.59 × 10−1 (mgTOC cm−2 h−1) for HA and 3.13 × 10−1 (mgTOC cm−2 h−1) for FA. The adsorption behavior of HA and FA on the copper surface is in accordance with the Langmuir adsorption isotherm. Langmuir adsorption constants measured were 5.98 × 10−2 L mg−1 for HA and 4.78 × 10−2 L mg−1 for FA. The copper foils exposed during five months to FA formed malachite deposits, whereas those exposed to HA did not and just cuprite was found. The results of this study showed that both HA as well as FA adsorption on copper surfaces is favored and no significant differences were found in the adsorption parameters calculated for both compounds. However, the inhibition of the malachite precipitation could be attributed to the HA adsorption.
Keywords: adsorption, copper, fulvic acid, humic acid