Effect of solution chemistry on cyanide adsorption in activated carbon

Coal is an important resource for the production of activated carbon. Among the numerous applications of activated carbon as a powerful adsorbent, the removal of anions from contaminated streams is one of the less investigated issues of industrial importance. A waste water pollutant of special interest is cyanide that attracts considerable concern due to its effects on humans and environment. Liquid phase adsorption is affected by various parameters, especially those concerning solution. The effects on cyanide adsorption capacity of the three most important parameters, namely solution temperature, pH and ionic strength, are investigated. Temperature enhances cyanide adsorption considerably, indicating an energy barrier in adsorption, most probably due to the hydration shell of cyanide ion. The optimum pH value is found to be 10 in accordance with carbon pHPZC value and cyanide pKa. Ionic strength effect demonstrated an outer sphere adsorption mechanism. From these effects it is concluded an adsorption mechanism based on electrostatic interaction between cyanide ion and positively charged carbon surface sites.