Determination of Extraction Period and Extractant Ratio for Extracting Humic Acid from Rice Straw Compost

Abstract

The process of isolating humic substances especially humic acid consumes a lot of time. The isolation (extraction, fractionation and purification) processes of humic acid from different sources such as soils, organic fertilizers and so on vary from 12 hours to 7 days. Based on the previous findings reported by other researchers, the standard extractant ratio used for humic acid extraction is 1:10 because it gives the highest yield of humic acid isolated. Previous studies tend to focus on the isolation duration of humic acid but not extractant ratio. To date, there is also lack of information about the extraction period and extractant ratio required to extract humic acid from rice straw compost. This study aimed to assess the minimum duration and extractant ratio for extracting humic acid from rice straw compost. A ratio of 1: 5 and 1: 10 of rice straw compost sample to chemical used were performed in humic acid extraction. A 5 g of rice straw compost sample was mixed with 25 mL and 50 mL of 0.5 M sodium hydroxide, respectively, and were extracted under different extraction periods (1, 3, 5, 7, 9, 12, and 24 hours). There was significant difference in the extraction periods and extractant ratio on the yield of humic acid. This study revealed that an extractant ratio of 1:10 and 12 hours of extraction period are required to extract humic acid from rice straw compost and can be purified within 1 hour using distilled water. Humic acid yield was significantly lower when the extraction period was less than 12 hours because the time was not sufficient for the H+ ions to displace Na+ ions and other cations. Furthermore, the difficulty of HA extraction period of less than 12 hours was probably due to difficulty of wetting the air-dried compost. The significance of this study is humic acid from rice straw compost can be isolated within 12 hour of extraction period, 24 hours of fractionation period and 1 hour of purification period under extractant ratio of 1:10. Thus, this may help in reducing time and costs needed to produce the humate product from this compost. The extractant ratio of 1:10 is more preferred because of the higher humic acid yield obtained.