Abstract
Developing an ideal and cheap adsorbent for adsorbing heavy metals from aqueous solution has been urgently need. In this study, a novel, effective and low-cost method was developed to prepare the biochar from lettuce waste with H3PO4 as an acidic activation agent at a low-temperature (circa 200 °C) hydrothermal carbonization process. A batch adsorption experiment demonstrated that the biochar reaches the adsorption equilibrium within 30 min, and the optimal adsorption capacity of Cd(II) is 195.8 mg∙g−1 at solution pH 6.0, which is significantly improved from circa 20.5 mg∙g−1 of the original biochar without activator. The fitting results of the prepared biochar adsorption data conform to the pseudo-second-order kinetic model (PSO) and the Sips isotherm model, and the Cd(II) adsorption is a spontaneous and exothermic process. The hypothetical adsorption mechanism is mainly composed of ion exchange, electrostatic attraction, and surface complexation. This work offers a novel and low-temperature strategy to produce cheap and promising carbon-based adsorbents from organic vegetation wastes for removing heavy metals in aquatic environment efficiently.
Highlights
Heavy metals are produced from different industries, such as industrial production, wastewater irrigation, and agriculture activities
During the batch adsorption experiment, a predetermined amount of biochar and 50 mL of solution with different Cd(II) initial concentrations were introduced in a 100 mL double-jacketed beaker, which was placed on the adsorption apparatus and stirred magnetically for 100 min to reach adsorption equilibrium
In summary, single-step hydrothermal synthesis of biochar from H3PO4-activation of lettuce waste was successfully accomplished in order to avoid traditional high-temperature pyrolysis
Summary
Heavy metals (with their density exceeding 5 g·cm−3) are produced from different industries, such as industrial production, wastewater irrigation, and agriculture activities. This study aims at preparing biochar adsorbents, with lettuce waste as raw material, via a single-step hydrothermal carbonization for removing Cd(II) ions from aqueous solutions effectively. HcHcoo33nnPPccOOeenn44-t-tarracaacttttiiiivoovannatssteedwwdbeebrriioeeocddchhiiassarpprlloaaobyybteetaaddiinniienneddFFaiiaggttuuddrrieieffssffeeSSrr11eeananttaahnnhyddyddSSrr22ooaatt,,hhrreeeerrssmmppaeeaclclttrriievveaaeeccllyytti.i.ooSSnniimmttiiimimllaaeerr aanndd aaccttiivvaattoorr cchhaarraacctteerriissttiicc ppeeaakkss wweerree oobbsseerrvveedd iinn tthhee FFTTIIRR ssppeeccttrraa ooff tthheessee bbiioocchhaarr ssiimmpplleess aass sshhoowwnn iinn FFiigguurree 22aa,, FS1igau, arensdSS12aaa. An aliquot of 0.05 g biochar adsorbent dosage was used to ensure full utilization rate of the adsorbent in subsequent adsorption experiment8so.fM20oreover, the increase in Cd(II) initial concentration has a significant impact on the adsorption capacity and removal efficiency of the LBC-P-1.3-200-2 sample (Figure 6c). The Cd(II) adsorption capacity was 97.32 mg·g−1 and the removal efficiency of Cd(II) ions was close to 98.69% when LBC-P-1.3-200-2 of 0.05 g was used as the adsorbent. The increase in Cd(II) initial concentration has a significant impact on the adsorption capacity and removal efficiency of the LBC-P-1.3-200-2 sample (Figure 6c). Follows: solution pH at 6.0, adsorbent dosage of 0.05 g, initial concentration of Cd(II) at 100 mg·L−1 and ambient adsorption temperature
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