Application of surface complexation modeling to trace metals uptake by biochar-amended agricultural soils

Alam, Mehboob; Swaren, Logan; Gunten, Konstantin von; Cossio, Manuel; Bishop, Brendan; Robbins, Leslie J.; Hou, Deyi; Flynn, Shannon L.; Ok, Yong Sik; Konhauser, Kurt O.; Alessi, Daniel S.

doi:10.1016/j.apgeochem.2017.08.003

Cited by 39 publications

(26 citation statements)

References 55 publications

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“…Over the past decade, our understanding of the mechanisms underpinning the adsorption of ions to geologic media has considerably improved through the use of sorption isotherms and experimentally-derived surface complexation modeling (e.g., Borrok and Fein, 2005;Alessi and Fein, 2010;Wang et al, 2010;Komárek et al, 2015;Liu et al, 2015;Alam et al, 2018;Liu et al, 2018;). Adsorption is generally governed by two parameters: the surface charge properties of the adsorbent and the chemical complexation of aqueous adsorbates onto specific surface functional groups (Dzombak and Morel, 1990).…”

Section: Introductionmentioning

confidence: 99%

Change of the point of zero net proton charge (pHPZNPC) of clay minerals with ionic strength

et al. 2018

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In a system where protons and hydroxide ions are the only aqueous species, the point of zero net proton charge (pHPZNPC) of a mineral defines the pH at which the positively and negatively charged functional groups on its surface are equal (Drever, 1997). Ascertaining the pHPZNPC of clay minerals, a ubiquitous component in soils, sediment and rivers, is useful in predicting its electrostatic interactions with charged aqueous species, colloids, and bacteria. While the pHPZNPC values of most clays have been reported, the variation of pHPZNPC with changing solution ionic strength (IS) and the mathematic relationship between them are not well-understood but critical in assessing the surface reactivity of clays in aqueous solutions ranging from freshwater to brines. To address this gap, we studied the relationship of the pHPZNPC of three clay minerals (kaolinite, illite, and montmorillonite) at seven ionic strengths (from 0.001 to 0.1 M). Titration data for each clay were used to calculate the pHPZNPC by two methods previously documented in literature: (1) using the difference between the blank titration and clay titrations, and (2) by the difference between the number of protons added during titration and the number of protons remaining in solution. The results show that: (1) unlike simple metal oxides (e.g., hematite, gibbsite, quartz), titration curves of clay minerals at different IS do not intersect at a common pHPZNPC value; (2) the pHPZNPC for kaolinite is around 5.6 to 6.6 while the pHPZNPC for illite and montmorillonite is in the range of 9 to10; (3) the pHPZNPC value decreases systematically with increasing IS for all three clay minerals studied; and (4) the change of pHPZNPC is linear with log(IS). A third method using surface complexation modeling (SCM) approach was applied to calculate the pHPZNPC of the clay minerals, and the results match well with Method 2. Our results allow for a more accurate estimation of clay surface charge property in aqueous environment, which, in turn, will improve model predictions of the adsorption of charged species in systems in which ionic strength changes.

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Section: Introductionmentioning

confidence: 99%

Change of the point of zero net proton charge (pHPZNPC) of clay minerals with ionic strength

et al. 2018

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“…To confirm this hypothesis and to gain access to the REE speciation on each biochar site types, the same modeling approach as already performed for humic substances was used ( Marsac et al., 2011 ). Modeling can account for changes in pH and ionic strength as already proposed by Alam et al. (2017) for cadmium and selenium.…”

Section: Resultsmentioning

confidence: 99%

Characterization of metal binding sites onto biochar using rare earth elements as a fingerprint

Pourret

Houben

2018

Heliyon

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The ability of biochar to immobilize metals relies on the amount of functional groups at its surface but the contribution of each functional groups (e.g. carboxylic, phenolic) to metal bonding is poorly known. Using a new approach based on previous works on rare earth element (REE) interactions with humic substances, we aim at elucidating the relative contribution of these binding sites to metal sorption under various conditions (i.e. pH and ionic strengths, IS). Using batch experiments, REE sorption onto biochar was analyzed from pH 3 to 9 and IS 10−1 mol/L to 10−3 mol/L. Rare earth element patterns show a Middle REE (MREE) downward concavity at acidic pH and low ionic strength. These patterns are in good agreement with existing datasets quantifying REE binding with humic substances. Indeed, the MREE downward concavity displayed by REE-biochar complexation pattern compares well with REE patterns with various organic compounds. This similarity in the REE complexation pattern shapes suggests that carboxylic groups are the main binding sites of REE in biochar. Overall, our results indicate that the strength of the metal bonding with biochar increases when pH and IS increase, suggesting that biochar is more efficient for long-term metal immobilization at near neutral pH and high ionic strength.

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“…The initial pH was set to 2.7 by adding 100 mM HCl and the samples were titrated with 100 mM NaOH from pH 2.7 to pH 11 followed by reverse titration with 100 mM HCl from pH 11 to 2.7 at a constant dispensing rate of 0.1 mL min −1 . To determine the acidity constants and the site concentrations of proton-active functional groups on the biochar colloids surfaces, titration data were modeled using the least-squared optimization software FITEQL 4.0, and a nonelectrostatic surface complexation modeling (NEM) approach (Alam et al 2018b).…”

Section: Characterizationmentioning

confidence: 99%

Biochar colloids and their use in contaminants removal

Safari

Gunten

Alam

et al. 2019

Biochar

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In this study, we report on the extraction, characterization, and potential applications of colloidal biochar derived from pyrolyzed wood-an untapped source of carbonaceous particles. A series of characterizations was performed on biochar colloids to unravel their colloidal properties and surface chemistry through which it was found that they have a net negative charge and are stable between pH 3 and 10. Moreover, our initial toxicity tests showed that biochar colloids themselves are not toxic and they can be used in remediation applications, which led us to investigate (1) their copper sorption, a model inorganic contaminant, in a scenario that biochar colloids are released into the environment and (2) their potential use in organic pollutants adsorption and degradation. Copper sorption studies showed that biochar colloids have a copper sorption capacity as high as 22 mg g −1 in sub-ppm copper solutions. This increased the acute 48 h lethal concentration (LC 50) of copper for Daphnia magna by 21 ppb, which is comparable to the previously reported effect by dissolved organic matter. Adsorption and degradation of methylene blue (MB), an often-used proxy for organic contaminants in water, were studied by coupling the biochar colloids to positively charged TiO 2 nanoparticles and using it as a photocatalyst. The hybrid MB photodegradation efficiency was 21% higher than that of TiO 2 nanoparticles alone. Enhancement of demethylation is proposed as the main degradation mechanism of MB, as confirmed by liquid chromatography-mass spectroscopy (LC/MS), and the positive impact of biochar colloids is ascribed to their abundant adsorption sites, which may facilitate MB adsorption and its photocatalytic degradation.

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Application of surface complexation modeling to trace metals uptake by biochar-amended agricultural soils

Cited by 39 publications

References 55 publications

Change of the point of zero net proton charge (pHPZNPC) of clay minerals with ionic strength

Change of the point of zero net proton charge (pHPZNPC) of clay minerals with ionic strength

Characterization of metal binding sites onto biochar using rare earth elements as a fingerprint

Biochar colloids and their use in contaminants removal

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