Effect of Processing Temperature on Membrane Ultrafiltration of Lignite coals-derived Humic Alkaline Extracts, Membrane Performance and Humic Acid Purity

Separation of inorganic materials and fulvate compounds from alkaline humate solutions is very important due to obtaining a better quality and more purified humic acid. For this reason, in this research a membrane separation system was used to separate fulvate compounds from humate solutions obtained from alkaline extraction of lignite coals (low rank coal). A hydrophilic ultrafilter membrane of polysulfone material with a pore size 5 kDa was employed using a plate and frame module. The effect of temperature (35, 45 and 55°C) on the membrane performance such as permeate flux of fulvates, fouling percentage, total membrane resistance and membrane resistance (RT and Rf), and morphology of membrane layers were investigated. Also, the influence of temperature on the humic acid purity obtained as retentate was determined using gravimetric analysis. The results of this work showed that by increasing the temperature from 35 to 55 °C, the value of permeate flux of fulvates was increased by 38%. Multiple behaviors were observed in the membrane fouling and resistances by increasing the temperature. The cake layer formation mechanism was obtained as dominant of fouling in 35°C temperature according to Hermia’s theoretical model results