Zinc Sorption in Calcareous Soils as Influenced by Biochar and Humic Acid: A Langmuir and Freundlich Isotherm Study

• Rebin, Mohammed Ahmed1, Hudhaifa, Al-Hamandi2

  Author

The study was conducted to evaluate the sorption behavior of zinc in three calcareous soils with different CaCO3 contents for three different samples amended separately with biochar and humic acid. Modeling of the adsorption properties was quantified by Langmuir and Freundlich models. Surface soil samples from Penjwen (low-Calcareous), Kani-Panka (medium-Calcareous), and Tasluja (High-Calcareous) soils were collected. Different doses of Biochar (0, 1 and 2%) and humic acid (0, 1 and 2%) were applied alone. The sorption of Zn on the material was measured using the batch equilibrium method and the experimental results were best fitted to the Langmuir and Freundlich models successfully described zinc sorption to estimate the values of Q max, KL, RL, MBC, KF, n and R². to the value of R2 is greater in freunlich Model than Langmuir Model, the Freundlich the highest average zinc sorption percentage was recorded in Soil (S1) treated with 1% biochar (54.22%), indicating a clear improvement in the soil's ability to retain zinc. In contrast, the lowest average sorption percentage (26.86%) was observed in Soil S3 treated with 2% humic acid, reflecting a reduction in sorption efficiency under this treatment. Soil (S2) exhibited intermediate values, with the highest average sorption percentage reaching 43.16% under 1% biochar. Overall, biochar treatments were more effective in increasing zinc sorption than humic acid treatments, particularly at the 1% application rate, whereas increasing the amendment rate to 2% did not consistently improve sorption efficiency. This indicates that the response depends on both the type of amendment and the calcium carbonate content of the soil.

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