A novel humic acid extraction procedure from Tunisian lignite

The present study investigates the efficient extraction of humic acid (HA) from Tunisian lignite (TL). The extraction method was optimized using the full factorial design (FFD) based on the interactive effects of sodium hydroxide (NaOH) and sodium pyrophosphate (Na 4 P 2 O 7 ) concentrations, extraction temperature, and agitation time as input factors. The output response was the absorbance ratio at 465 and 665 nm ( E 465 / E 665 ) of HA. Fourier-transformed infrared (FT-IR), was used for the characterization of TL-HA. Under optimized conditions (NaOH of 0.8 mol l −1 , Na 4 P 2 O 7 of 0.06 mol l −1 , a temperature of 85 °C and an agitation time of 6 h), the obtained lignite-based fertilizer contains a high HA’s aromaticity degree as evidenced by the lower ratio ( E 465 / E 665 ) with a value equal to 1.34. The TL-HA characterization shows the predominance of OH, COOH, CH, C=C and COO groups, which are typical functional groups in humic substances. The effects of this new humic acid (HA) source on wheat germination and root elongation were investigated. The results showed that the wheat seeds germinated in HA fertilizer diluted 20 times produced high germination percentage. Indeed, the addition, of diluted HA, increased the elongation rate of the wheat roots up to 120% compared to the controls. The results of the present study might be useful for practical and commercial applications of this fertilizer based on its humification parameters and its conformity to Tunisian legislation. To investigate the limits of this alkali exaction method, large-scale processes experiments are still necessary.