Abstract
Seaweed biochar is an efficient alternative bioadsorbent for Cu2+ removal due to its low cost and heavy metal removal capacity. Using the slow pyrolysis process, we produced biochars from Macrocystis pyrifera at 300 (BC300), 450 (BC450), and 600 °C (BC600). The physicochemical and structural properties of the biochar samples improved with increasing pyrolysis temperature from 300 to 450 °C, whereas no significant differences were observed with further increases in temperature to 600 °C. The yield ranged between 49% and 62% and had a high ash content (57.5–71.1%). BC450 and BC600 presented the highest surface areas and higher porosities. The FTIR spectra indicated that an increase of temperature decreased the acidic functional groups due to depolymerization and the dehydration processes, increasing the aromatic structures and the presence of calcium carbonate. The fittings of the kinetic models were different for the BCs: for the BC450 and BC600 samples, the Cu2+ adsorption was well-represented by a pseudo-first-order model; for BC300, a better fit was obtained with the pseudo-second-order model. The rate-limiting step of Cu2+ adsorption on BCs was represented by both models, liquid film diffusion and intraparticle diffusion, with surface diffusion being more important in BC300 and BC600, and intraparticle diffusion in BC450, in agreement with the pore size of the biochar samples. The adsorption isotherms of all BCs showed Langmuir behavior, representative of a chemisorption process, which was corroborated by the energy adsorption values determined by the D–R model. The maximum monolayer Cu2+ adsorption capacities were 93.55 and 58.0 mg g−1 for BC600 and BC450, respectively, whereas BC450 presented the highest affinity. Other mechanisms involved in controlling heavy metal removal from aqueous suspensions using these seaweed biochars remain to be explored. We conclude that BC450 and BC600 from M. pyrifera are the most efficient adsorbents for Cu2+ aqueous removal and are thus an appropriate alternative for bioremediation.
Highlights
Anthropogenic inputs of heavy metals into the environment pose a serious threat to humanity and ecosystems worldwide due to their toxicity, persistence, and bioaccumulation [1,2]
This tendency is consistent with that observed in other studies; the weight loss at each pyrolysis temperature differs according to the source material [15,17,26]
Biochars were generated from Macrocystis pyrifera for the first time through a slow pyrolysis process at three temperatures (300, 450, and 600 ◦C), obtaining high yields, high ash contents, and the presence of calcium carbonate in all biochar samples
Summary
Anthropogenic inputs of heavy metals into the environment pose a serious threat to humanity and ecosystems worldwide due to their toxicity, persistence, and bioaccumulation [1,2]. Heavy metals, which are some of the most serious pollutants, derive from both industrial sources and domestic discharge, affecting environmental quality and human health [3]. The main sources of heavy metal pollution in water and soils are industrial wastes, agricultural pesticides and fertilizers, and domestic wastewater [2,3,4,5]. Copper is a relevant environmental pollutant released from diverse anthropogenic sources, such as industrial and mining activities, combustion processes, the production and use of phosphate-based fertilizers, and domestic wastewater discharge. Copper uptake in humans primarily occurs from the ingestion of polluted food and water, mostly in the form of Cu2+. An excess of copper is toxic due to its displacing other metallic cofactors [5]
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