Competitive Adsorption of Li+, Na+, and K+ Ions on Phillip Site/Chabazite Zeolitic Tuff from Jordan

The adsorption of alkali metal ions on zeolite has no such possibility of precipitation. In the current work, we have studied the adsorption isotherms, and the effect of pH and temperature on the adsorption of alkali metals (Li+, Na+, K+) onto Jordanian zeolitic tuff (phillipsite and chabazite) using batch adsorption method. Fitting the data using the competitive Langmuir adsorption model indicates that adsorption capacity of Li+, Na+, and K+ are 4.9, 3.4, and 2.7 mmol/g, respectively. The results showed that adsorption of alkali metals on zeolite decreases with increasing pH and temperature which is a distinct behavior from that of heavy metals. The ΔH values of adsorption process are -85.6, -23.4, and -41.5 kJ/mol for initial concentrations of K+, Li+, and Na+, respectively. The calculated ΔS values are -0.285, -0.081, and -0.132 J/mol.K, for the same list of metals, respectively. The negative and decreasing entropy values associated with the adsorption process indicate that zeolite may encapsulate alkali metal ions in pores rather than ion exchange. The current investigation suggests the possible use of natural zeolite for seawater’s desalination by trapping alkali metals in the pores.