Assessment of the Effect of Organic Matter on the Retention of Pb+2 in Artificial Soils
2021
Sánchez-Andica, Rubén Albeiro | Chamorro-Rengifo, Andrés Felipe | Páez-Melo, Martha Isabel
Four artificial soils (AS) were prepared based on a mixture of humus, bentonite, kaolinite, and polyvinyl chloride (PVC), as inert matter, in the following proportion: 0%, 12.44%, 37.50%, 78.55% of humus, 10.5% of bentonite, 10.5% of kaolinite, and 78.92%, 66.26%, and 41.46% of PVC. The AS were prepared with variable content of organic matter (OM) in order to evaluate the retention of lead (II) due solely to the content of OM. The results indicated that retention capacity of Pb⁺² increases (19.74 mg/g, 20.89 mg/g, 61.61 mg/g, and 79.48 mg/g) as OM increases (0%, 1%, 5%, and 10%); however, this retention is not proportional to the OM increment. An increase of background solution concentration of 0.01 M to 0.1 M resulted in a 50% decrease in the lead retention capacity. The fitting of lead adsorption was performed by the regression coefficient (R²). All R² of the Langmuir model fit successfully to all types of AS (0.973 for 10-OM, 0.9845 for 5-OM, 0.999 for 1-OM, 0.994 for 0-OM). The adsorption kinetics also fits well to the pseudo-second-order model (R²₁₀₋OM = 0.989, R²₅₋OM = 0.999, R²₁₋OM = 0.999, and R²₀₋OM = 0.999). The thermodynamic values of the Gibbs free energy (ΔG⁰₁₀₋OM = − 10.62, ΔG⁰₅₋OM = − 11.50, ΔG⁰₁₋OM = − 14.23, and ΔG⁰₀₋OM = − 17.06) indicated that it was a spontaneous process, and the energy of the process suggests a retention mechanism by ion exchange. A soil with high content of OM does not guarantee high retention of lead, even more so when the adsorption mechanism is given by ion exchange.
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