Mechanisms of the removal of hexavalent chromium by biomaterials or biomaterial-based activated carbons

Application of Brazilian-pine fruit coat as a biosorbent to removal of Cr(VI) from aqueous solution—Kinetics and equilibrium study

“…Taking into account the kinetic experiments (the chemisorption kinetic model very well fitted, the pseudo-second-order kinetic model suitably fitted and also the three stages of the intraparticle diffusion kinetic model) associated with the desorption experiments and also considering the other papers related with the biosorption of Cr(VI) [9,40,41] on different biosorbents, there are several arguments to propose that the mechanism of Cr(VI) biosorption, can be attributed to the reduction of Cr(VI) to Cr(III) promoted by the phenolic contents present on the PW followed by the chelation of Cr(III) with the oxidized organic compounds, as depicted on Scheme 1. It should be taken into account that the reduction process occurs only at biosorbent surface, as already reported [9], where no formation of Cr(III) in the adsorbate solution was detected [9,18].…”

“…polyphenols (step 1), H + ions were consumed. The polyquinone formed in the first step formed a complex with the Cr 3+ (step 2) [9,40,41]. The chromium uptaken by the PW could only be released by the presence of H 2 O 2 in basic medium, that oxidizes Cr(III) to Cr(VI) [31].…”

Preparation of Amidoxime Adsorbent by Radiation Induced Grafting of Acrylonitrile on Polyethylene Film and Its Application in Cr(VI) Removal

“…15 For this purpose, many types of adsorbents have been investigated for the removal of chromium including activated carbon, biomaterials and nanomaterials. [15][16][17][18][19][20][21][22][23][24] Recently, many researchers have focused attention on grafted polymers as alternative heavy metal adsorbent. [25][26][27][28][29][30][31][32][33][34][35] "Grafting" is a method in which functional monomers are covalently bonded onto the backbone polymer chain.…”

Evaluation of the Combined Cr(VI) Removal Capacity of Sawdust and Sawdust-Immobilized Acinetobacter haemolyticus Supplied with Brown Sugar

“…This was due to the negligible volume of micropores and the low surface area of the URWS as described earlier in Section 2.2. Cr(VI) can be removed from the aqueous solution by nonliving biomass such as URWS via two mechanisms (Park and Park 2006). The first mechanism involves direct reduction of Cr (VI) to Cr(III) in the aqueous phase by contact with the electron-donor groups on the biomass having lower reduction potential values than +1.3 V, i.e., that of Cr(VI) (Katz and Salem 1994).…”

“…If there are a small number of electron-donor groups in the biomass or protons in the aqueous phase, the chromium bound on the biomass can remain in the hexavalent state (Mohan and Pitmann Jr. 2006). At any given time, these two mechanisms would occur concurrently depending on the parameters involved such as pH, temperature, biomass concentration, functional groups present on the biomass, and Cr(VI) concentration (Park and Park 2006). Hence, it is rather inappropriate to address the mechanism occurring during the contact between Cr(VI) and URWS simply as "adsorption" or "reduction" because both reactions occur at the same time.…”