As a salt adsorbent, biochar could remove/isolate salt ions e.g. Na through physiochemical adsorption to mitigate the salinity of brackish water, but little is known about its magnitude and mechanisms. The current study aimed to examine the effects of biochar on: (1) Na-adsorptive capacity and mechanism and (2) Electrical Conductivity (EC) and K displacement. Six pyrolysis temperatures (250, 350, 450, 550, 650, and 750ºC) were applied to produce biochars from rice husk. The biochars were then used as adsorbents to adsorb Na from salty water varying in NaCl concentrations. The Langmuir isotherm Model (LMM) and Dubinin-Radushkevick isotherm Model (DRM) were used to quantify the dependence of adsorbed Na on Na concentration at equilibrium. The LMM quantification revealed that the maximum Na-adsorptive capacity of biochars increased from 25.8 to 67.8 (mg g^-1) upon increased temperatures. The EC was reduced and the K amount displaced from biochar was increased with an increase in pyrolysis temperature. The DRM quantification revealed that the Na-adsorptive mechanism was mainly a physical process. A significant relationship between the Na amount adsorbed and the K amount displaced from biochar suggested that the ion-exchange mechanism could co-exist. In brief, the findings indicated that the salinity of the brackish water could be significantly mitigated by the biochar treatment through mainly physical adsorption leading to a reduced EC and increased K: Na ratio.

Keywords: Dubinin-Radushkevick model, Langmuir isotherm, Saline soils, Sodium adsorption.

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