Influence of Acids on Morphology of the Surface of Soil Colloidal Particles and Chemical Properties.

In this study, we investigated influence of acids on morphology of the surface of soil colloid particles and chemical properties for soils collected from the subsurface of forest stand. To do this, soil samples were treated with several acids such as H₃PO₄, H₂SO₄, HF and HNO₃. 100 ml of the five levels of HF concentrations ranging from 0% to 7.5% were applied and thoroughly mixed with 50 g of soil samples with soils. Then soil samples left at room temperature for 24 hr were oven dried at 105 °C for another 24 hr after removing soil solution using vacuum filtration. For these soil samples, we analyzed the cation exchange capacity (CEC), pH, electrical conductivity, and particle size. Apart from these soil samples, we also measured the exchangeable and water-soluble cations in the extracts obtained from filtration using inductively coupled plasma-optical emission spectrometer (Varion Vista-MPX, Australia), Morphologies of the surface of soil colloid particles were analyzed by scanning electron microscope (SEM) and x-ray diffraction (XRD). The results showed that HF was the most violent reactant compared with other three acids. The soil color became generally brighter with concentration acids, especially on HF, and H₂SO₄. pH and EC of the soil were rapidly decreased as the concentrations of the acids increased. The CEC was increased with increasing concentrations of the acids from 12.8 cmol₍₊₎ kg^-1 for 0% of HF to 134 cmol₍₊₎ kg^-1 for 48% of HF. In swelling index, the highest value was shown in 48% H₂SO₄ treatment soil. The soil samples showed that swelling index for 48% H₂SO₄treatment was almost 2.29 than that of the control treated with distilled water. ESEM results for the acid treatments clearly showed that there was expansion between the layers of clay particles treated with HF and sulfuric acids.