Latest development in the fabrication and use of lignin-derived humic acid

Abstract

Humic substances (HS) are originated from naturally decaying biomass. The main products of HS are humic acids, fulvic acids, and humins. HS are extracted from natural origins (e.g., coals, lignite, forest, and river sediments). However, the production of HS from these resources is not environmentally friendly, potentially impacting ecological systems. Earlier theories claimed that the HS might be transformed from lignin by enzymatic or aerobic oxidation. On the other hand, lignin is a by-product of pulp and paper production processes and is available commercially. However, it is still under-utilized. To address the challenges of producing environmentally friendly HS and accommodating lignin in valorized processes, the production of lignin-derived HS has attracted attention. Currently, several chemical modification pathways can be followed to convert lignin into HS-like materials, such as alkaline aerobic oxidation, alkaline oxidative digestion, and oxidative ammonolysis of lignin. This review paper discusses the fundamental aspects of lignin transformation to HS comprehensively. The applications of natural HS and lignin-derived HS in various fields, such as soil enrichment, fertilizers, wastewater treatment, water decontamination, and medicines, were comprehensively discussed. Furthermore, the current challenges associated with the production and use of HS from lignin were described.

Accessing the Low-Polar Molecular Composition of Boreal and Arctic Peat-Burning Organic Aerosol via Thermal Analysis and Ultrahigh-Resolution Mass Spectrometry: Structural Motifs and Their Formation

“…This second mass loss step might be attributed to peat compounds with a more stable carbon skeleton requiring higher temperatures for combustion. Those species might be humic substances, a broad group of larger soil organic compounds formed by microbial degradation of lignocellulosic biomass, which is characterized by functionalized, bridged, and higher aromatic molecular structures. ,,, Therefore, we assume that the second mass loss step observed under oxidative combustion conditions could result from the combustion of larger aromatic structures of humic substances with higher humification degree. The idea of increased microbial matured compounds is further supported by the TGA data of the same peat sampled in greater depth as shown in Figure S6 (Table S5).…”

Lignins as Promising Renewable Biopolymers and Bioactive Compounds for High-Performance Materials

“…To convert lignin into humic-like materials, alkaline aerobic oxidation, alkaline oxidative digestion, and oxidative ammonolysis of lignin are applied. The obtained humic substances are useful in soil enrichment, fertilizers, wastewater treatment, water decontamination, and medicine [150,151].…”

Ultrasound‐Assisted Synthesis of Humic‐Silica Composites by the Isolation of Humic Substances from Peat and Lignite

“…The main step of the procedure for the isolation of humic substances includes the alkaline extraction from natural raw materials such as peat, lignite, leonardite, sediments, or compost. [3,4,5] After extraction, for the separation of humic acids (HA) from fulvic acids (FA), the pH of the extract is reduced to approximately 1, typically with the use of a HCl solution. [6] Both humic and fulvic acids were analyzed in detail in terms of their use in agriculture.…”

“…Generally, humic substances can be divided into fractions that differ in solubility in different pH ranges. The main step of the procedure for the isolation of humic substances includes the alkaline extraction from natural raw materials such as peat, lignite, leonardite, sediments, or compost [3,4,5] . After extraction, for the separation of humic acids (HA) from fulvic acids (FA), the pH of the extract is reduced to approximately 1, typically with the use of a HCl solution [6] .…”