Related Experiment Video
Updated: Nov 12, 2025
Quantification of Humic and Fulvic Acids in Humate Ores, DOC, Humified Materials and Humic Substance-Containing Commercial Products
Published on: March 18, 2022
Mechanism and multi-step kinetic modelling of Cr(VI) adsorption, reduction and complexation by humic acid, humin and
Samuel Barnie1,2, Jia Zhang3, Peter Appiah Obeng2
1Beijing Key Laboratory of Water Resources and Environmental Engineering, China University of Geosciences, Beijing, 100083, China.
Abstract:
Humin (HM) and kerogen (KG) are widespread in soils and sediments, which have strong retention effects on the migration and transformation of Cr(VI) in subsurface environment. Previous studies mainly focused on the interaction between Cr(VI) and soluble organic matter, such as humic acid (HA); however, the adsorption and reduction mechanism for Cr(VI) by insoluble HM and KG are still unclear, the processes of which might be quite different from HA due to their different sources and humification degrees. Consequently, in this study, HA, HM and KG extracted from different sources were used to explore the adsorption, reduction and complexation mechanisms of Cr(VI) in soils and sediments, based on which a multi-step kinetic model of Cr(VI) was carried out. According to the results, the retention of Cr(VI) by humus was found to obey a coupling mechanism of "adsorption-reduction-complexation", where Cr(VI) adsorption was by complexation with carboxylic groups by ligand exchange. The phenolic and hydroxylic groups were determined to be the main electron donor for Cr(VI) reduction. Notably, the Cr(III) produced was found to be adsorbed on the surface of humus by complexation on phenolic and hydroxylic groups, and the excesses were released into the liquid phase after the saturation of complexation sites. Based on the revealed mechanism, a multi-step kinetic model for simultaneously describing Cr(VI) adsorption and reduction and behaviour of Cr(III) was proposed producing a better fitting performance (R2 ≥ 0.984) than the first-order and second-order kinetic models (R2 ≤ 0.84 and 0.87, respectively) and hence could provide more factual understanding of Cr(VI) transformation in soils and sediments enriched in various types of humus.
More Related Videos
11:14Two-way Valorization of Blast Furnace Slag: Synthesis of Precipitated Calcium Carbonate and Zeolitic Heavy Metal Adsorbent
Published on: February 21, 2017
10:44Preparation of Biomass-based Mesoporous Carbon with Higher Nitrogen-/Oxygen-chelating Adsorption for CuII Through Microwave Pre-Pyrolysis
Published on: February 12, 2019
Related Concept Videos
02:31Multi-Step Reactions
03:06Reaction Mechanisms
For instance, the decomposition of ozone appears to follow a mechanism with two steps:
02:46E1 Reaction: Kinetics and Mechanism
02:13Reduction of Alkenes: Catalytic Hydrogenation
Metals like palladium, platinum, and nickel are commonly used in their solid forms — fine powder on an inert surface. As these catalysts remain insoluble in the reaction mixture, they are referred to as heterogeneous catalysts.
The hydrogenation process takes place on the...
02:45E2 Reaction: Kinetics and Mechanism
03:08Rate-Determining Steps
In a multistep reaction mechanism, one of the elementary steps progresses significantly slower than the others. This slowest step is called the rate-limiting step (or rate-determining step). A reaction cannot proceed faster than its slowest step, and hence, the rate-determining step limits the overall reaction rate.
The concept of rate-determining step can be understood from the analogy of a 4-lane freeway with a short-stretch of traffic-bottleneck caused due to...