Leonardite are a natural material that is used for agriculture. Since, leonardite has a majority compoment such as silica and humus compounds, especially humic substances consisting of fulvic acid, humic acid, and humin. In this research, the amount of adsorbent, the contacting time, and the concentration of adsorbate were studied. The optimized conditions were 3 g of leonardite, 4 hr for contacting time, and 200 mg/L of chlorate. The percentage of chlorate adsorption by leonardite was 8.57. While, the adsorbent was the mixture of leonardite and kaolin in amount of 3 g, 4 hr for contacting time, and 200 mg/L of chlorate provided 6.94 percentage of adsorption. Leonardite could be a bit more ability to adsorb chlorate than leonardite mixed with kaolin. Further, leonardite was studied to adsorb nitrogen, phosphorus, and potassium. They were 1.2, 1.6, and 9 mg/L per 1 g of leonardite. The percentage of adsorption were 99.06, 72.74 and 93.14, respectively. In case of desorption, 0.12, 0.18, and 0.15 mg/L per 1 g of leonardite. The percentage of desorption were 9.95, 18.24, and 8.05, respectively.
The soil was collected from the Pakham village, PaKham District, Muang, Lamphun Province. It was determined the amount of chlorate before treated with leonardite. The amount of leonardite was decrease 25 % in the first week. The percentage of chlorate was decreased as 7 and 3 in each one week later.