Abstract
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One of the most advantageous methods for lowering water hardness is the use of lowcost
adsorbents. In this research, the effectiveness of natural zeolite (clinoptilolite type), activated
carbon, and activated alumina was evaluated. These adsorbents were sequentially modified by
NaCl, HCl, and NaCl-HCL to improve their ability to adsorb. The contact time and the amount of
adsorbent used in the adsorption process were investigated experimentally to determine their effects.
The results indicated that the best contact time for hardness reduction was 90 min, and the best
concentrations of adsorbents in drinking water for zeolite, activated carbon, and activated alumina
were 40, 60, and 60 g/L, respectively. In addition, for groundwater, these figures were 60, 40, and
40 g/L, respectively. The greatest possible decreases in total hardness under the best conditions by
natural zeolite, activated carbon, and activated alumina adsorbents were 93.07%, 30.76%, and 56.92%,
respectively, for drinking water and 59.23%, 15.67 %, and 39.72% for groundwater. According to the
results obtained from experiments, NaCl-modified zeolite, natural zeolite, and NaCl-HCl-modified
activated carbon performed better in terms of parameter reduction. The equilibrium data were well
fitted by the Langmuir isotherm model, whereas the kinetic data for the adsorption process were
consistent with the pseudo-second-order model. The equilibrium study of the adsorption process by
the Morris–Weber model revealed that both chemical and physical adsorption are involved.
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