Unraveling the mechanisms of lead adsorption and ageing process on high‐temperature biochar

Abstract

BACKGROUND The synthesis gas or hydrogen‐rich gas, at longer residence times and higher temperatures, is frequently the target of pyrolysis biomass. Biochars obtained at such conditions contain less functional groups but they are more effective for longer‐term soil C storage. The aim of this study was to elucidate the adsorption mechanisms and the effect of the ageing process on high‐temperature biochar towards lead adsorption. The biochars under study were produced from the pyrolysis of almond wood and olive tree pruning. RESULTS The almond hardwood biochar was the most susceptible to the oxidation process. This biochar exhibited higher carbon loss than the olive biochar, 22.07% and 11.76%, respectively. The adsorption process was better described by the Langmuir model and pseudo‐second order kinetics. The maximum adsorption capacity decreased from 40.3 to 24.8 mg g–1 after the oxidation process for almond‐derived biochar and remained unchanged for the olive‐biochar. Analyses demonstrated that 67% of the adsorbed Pb2+ was removed through complexation by oxygen functionalities and phosphorous compounds. After the oxidation process, this fraction accounted for only 45% of the adsorbed Pb2+, ion exchange and cation‐π being the most prominent mechanisms for the adsorption. CONCLUSION Biochar oxidation could cause the mobilization of 30% of the adsorbed lead under acid conditions. Special attention should be given to biochar's intrinsic properties, such as O/C and H/C ratio, for the application of these materials in the treatment of contaminated soil. High‐temperature biochars would offer the additional advantage of managing the remediation of scenarios with low pH. © 2020 Society of Chemical Industry (SCI)

Inversion of loading‐implicit adsorption isotherms by means of the Lambert W function

“…A modified form of Langmuir's kinetic argument for saturable adsorption of gases to solid surfaces was used to derive the Elovich isotherm, given here by Eqn (3). 19,20 In Eqn (3), k E is an equilibrium constant, while q E is the apparent saturation capacity. A linear form of the Elovich isotherm is commonly used to correlate water contaminant adsorption data.…”

“…The linear fit of Eqn (7) was not satisfactory, returning an R 2 score of 0.92. Here, we will convert the loading-implicit Elovich isotherm [Eqn (3)] to an explicit form and fit the resulting expression to the cobalt adsorption data. Inverting the loading-implicit Elovich isotherm by means of the Lambert W function is quite straightforward.…”

“…[31][32][33] In a recent article, the Elovich isotherm, written in the form of Eqn (13), was used to fit the experimental isotherms for uranium(VI) adsorption on two adsorbents (leonardite and humic acid derived from leonardite). 34 Equation ( 13) is, of course, just a rearranged form of Eqn (3).…”

“…Commonly used isotherm models include the equations of Langmuir, Freundlich, Sips, and Dubinin-Radushkevich. [1][2][3] Many software packages, including Excel, 4 offer standard nonlinear regression methods to fit these isotherm equations to experimental data. The conventional nonlinear regression procedure minimizes the sum of squared residuals (SSR) using a fitting algorithm.…”

“…Experimentally measured isotherms for water contaminant adsorption on solid materials are generally correlated using suitable theoretical or empirical models. Commonly used isotherm models include the equations of Langmuir, Freundlich, Sips, and Dubinin—Radushkevich 1‐3 . Many software packages, including Excel, 4 offer standard nonlinear regression methods to fit these isotherm equations to experimental data.…”