Thermal Na+ conditioning of natural clinoptilolite for softening removal of aqueous Ca2+ from simulated cooling-water environment

Na+-conditioned clinoptilolite (NaCC) was evaluated as an efficient softener dealing with aqueous Ca2+ in cooling-water environments. Thermal Na+ conditioning largely improved the softening capability of natural clinoptilolite, and the uptake of Ca2+ interestingly accelerated as solution temperature increased up to a level of 70 degrees C (simulating spent cooling water). Batch study on fundamental parameters indicated that the adsorption kinetics and isotherms using NaCC could, respectively, be expressed by pseudo-first-order model and Langmuir equation. Ion exchange was determined as principal softening pathway being thermodynamically spontaneous and endothermic. In continuous column test, the breakthrough curves completed by NaCC can appreciably be delineated by Thomas and Yoon-Nelson models, demonstrating the viability on prediction of the equilibrium adsorbability and durability as significant operative parameters. Moderate pH level exhibited suitable enough for both the functionality and repeated use of NaCC. As a result of preliminary tests, Na+ conditioning of clinoptilolite may be recommended as effective softening strategy serving for industrial cooling-water systems.