Partition of humic acids using alkaline aqueous two-phase systems constituted of alcohol and hydroxides

BACKGROUND: Humic acids (HAs) are macromolecules classified within the group of humic substances that are mainly related to the agricultural and environmental sectors, but they have attracted interest from the medicine, pharmaceutical and cosmetic industries. However, these latter sectors depend on developing extraction and purification technologies for adequate use. Thus, this paper aims to study the partitioning and recovery of HA using alkaline two-phase aqueous systems (ATPSs) based on alkali metal-based hydroxides and alcohols. Initially, the influence of alcohols (methanol, ethanol, 1-propanol, and 2-propanol) and hydroxides [sodium (NaOH), potassium (KOH) and lithium (LiOH)] in the phase diagrams construction was addressed. RESULTS: The phase formation is correlated to an increase in the hydrophobicity of alcohols and hydroxides, which allows for the enlargement of the biphasic region. In the proposed systems, HA is always partitioned to the hydroxide-rich phase. Increasing the hydrophobicity of the alcohol favors the migration of HA to the opposite phase, while increasing the hydrophilicity of the hydroxides leads to better partition and recovery values. It was observed that increasing TLL favors the recovery of HA. Furthermore, there was a decrease in alcohol concentration in the hydroxide-rich phase with an increase in the alkyl chain and TLL, improving the recovery. Finally, the best reached-recovery value was 98.18 +/- 0.41% (KHA = 0.038 +/- 0.02) for ATPS formed by 1-propanol + NaOH with TLL approximate to 55 at 298 K. CONCLUSIONS: Alkaline systems can be a novel route for recovering humic substances from the environment. (c) 2024 Society of Chemical Industry (SCI).