Enhanced SO2 adsorption and desorption on chemically and physically activated biochar made from wood residues

SO2, one of the most harmful gases, is generated when oxygen in air combines with sulfur species from anthropogenic sources (e.g., the smelting of mineral ores). Thus, the objectives of this study are to assess the potential use of activated biochar for the removal of SO2, and to compare the impact of the activation process on the development of porosity and surface chemistry for SO2 adsorption. Results show that activated biochars develop porosity (with narrow and wide pores) and functional groups connected to their surface, which makes these materials suitable for adsorption of SO2. However, no linear relationship between textural properties and the amount of SO2 adsorbed by activated biochars from dynamic adsorption tests were noticed. In addition, the highest SO2 adsorption capacity was not reached for materials with the highest surface area, or micropore or ultramicropore volume. Specifically, steam-activated biochar had the best performance for the removal of SO2 due to its optimal surface area (590 m2 g−1); volume of ultra- (0.22 cm3 g−1), micro- (0.23 cm3 g−1), and mesopores (0.11 cm3 g−1); its basic character (not from nitrogenated groups); and the low percentage of acid-oxygenated functional groups connected to its surface. After six thermal regeneration cycles, activated biochar exhibited high SO2 removal capacity and high regenerability. Based on these findings, activated biochar made from forest wood residues has promising potential for the removal of gas contaminants

Production, characterization and application of activated biochar from wood residues

Biochar is a carbon-rich material characterized by physicochemical properties desirable in multi-disciplinary areas of science and engineering such as waste management, soil amendment, carbon sequestration, bioenergy, and degraded sites rehabilitation. However, the porosity and surface area of such materials are often very low. For example, the surface area of white birch biochar obtained by fast pyrolysis at 450°C, does not exceed 5 m2 g-1. Recently, there is growing interest of the research and industrial communities in converting biochar into activated biochar due to: i) its low-cost availability; ii) potential economic feasibility in large-scale production; and iii) its effectiveness in several applications such as the treatment (sorption) of drinking water and wastewater, energy storage, as electrodes in batteries and supercapacitors, and as catalyst support. Please click on the file below for full content of the abstract

Activated Biochar as an Effective Sorbent for Organic and Inorganic Contaminants in Water

Adsorption is acknowledged as effective for the removal of pollutants from drinking water and wastewater. Biochar, as a widely available material, holds promises for pollutant adsorption. So far, biochar has been found to be effective for multiple purposes, including carbon sequestration, nutrient storage, and water-holding capacity. However, its limited porosity restricts its use in water treatment. Activation of biochars, when performed at a high temperature (i.e., 900 °C) and in the presence of certain chemicals (H3PO4, KOH) and/or gases (CO2, steam), improves the development of porosity through the selective gasification of carbon atoms. Physicochemical activation process is appropriate for the production of highly porous materials. As well, the morphological and chemical structure of feedstock together with pyro-gasification operating conditions for the biochar production can greatly impact the porosity of the final materials. The effectiveness of activated biochar as adsorbent depends on porosity and on some functional groups connected to its structure, both of these are developed during activation. This study provides a comprehensive synthesis of the effect of several activated biochars when applied to the treatment of organic and inorganic contaminants in water. Results show that high aromaticity and porosity are essential for the sorption of organic contaminants, while the presence of oxygen-containing functional groups and optimum pH are crucial for the sorption of inorganic contaminants, especially metals. Finally, although activated biochar is a promising option for the treatment of contaminants in water, further research is required to evaluate its performance with real effluents containing contaminants of emerging concern

Performance of Physically and Chemically Activated Biochars in Copper Removal from Contaminated Mine Effluents

The increasing global demand for metals and minerals justifies the intensive study of treatment options for contaminated mine effluents. The present study evaluated the conversion of wood residues into physically and chemically activated biochars and their subsequent use in the treatment of Cu in synthetic and actual contaminated mine drainage. First, wood residues were converted into biochar by fast pyrolysis. Then, physical (using steam or CO2) or chemical (using KOH) activation was carried out in a homemade pilot-scale furnace. After activation, highly microporous (KOH materials) and micro/mesoporous activated biochars (CO2 and steam materials) were obtained. Batch adsorption testing was first conducted with synthetic effluents. Results showed that CO2-activated biochar was the most Cu effective adsorbent (99% removal) at low concentrations (5–20 mg L−1). The mechanisms of Cu2+ adsorption involved physical and chemisorption for biochars and CO2-activated biochar, while chemisorption for KOH-activated biochars was probably due to the high proportion of functional groups connected to their surface. In multi-metal acid mine drainage, metal adsorption capacities deteriorated for most of the materials, probably due to the effects of ion competition. However, KOH-activated biochar decreased Cu2+ concentrations to below the authorized monthly mean allowed by Canadian law (0.3 mg L−1) and decreased Co, Pb, and Mn concentrations up to 95%. These findings indicate that high porosity and oxygenated functional groups connected to the surface of activated biochars are important properties for the enhancement of interactions between carbon materials and metals from mine effluents, as well as for their performance improvement in mine drainage treatment

Production, characterization, and potential of activated biochar as adsorbent for phenolic compounds from leachates in a lumber industry site

There is growing interest in low-cost, efficient materials for the removal of organic contaminants in municipal and industrial effluents. In this study, the efficiency of biochar and activated biochar, as promising adsorbents for phenol removal, was investigated at high (up to 1500 mg L−1) and low concentrations (0.54 mg L−1) in synthetic and real effluents (from wood-residue deposits in Québec), respectively. The performance of both materials was then evaluated in batch adsorption experiments, which were conducted using a low solid/liquid ratio (0.1 g:100 mL) at different phenol concentrations (C0 = 5–1500 mg L−1), and at 20 °C. Activated biochars presented higher phenol adsorption capacity compared to biochars due to their improved textural properties, higher micropore volume, and proportion of oxygenated carbonyl groups connected to their surface. The sorption equilibrium was reached within less than 4 h for all of materials, while the Langmuir model best described their sorption process. The maximum sorption capacity of activated biochars for phenol was found to be twofold relative to biochars (303 vs. 159 mg g−1). Results also showed that activated biochars were more effective than biochars in removing low phenol concentrations in real effluents. In addition, 95% of phenol removal was attained within 96 h (although 85% was removed after 4 h), thus reaching below the maximum authorized concentration allowed by Québec’s discharge criteria (0.05 mg L−1). These results show that activated biochars made from wood residues are promising potential adsorbent materials for the efficient treatment of phenol in synthetic and real effluents

Influence of Pyro-Gasification and Activation Conditions on the Porosity of Activated Biochars: A Literature Review

Biochar is a carbon-rich organic material that has advantageous physicochemical properties for applications in multidisciplinary areas of science and engineering, including soil amendment, carbon sequestration, bioenergy production, and site rehabilitation. However, the typically low porosity and surface area of biochars (from 0.1 to 500 m2 g−1) limits the suitability for other applications, such as catalysis, electrochemistry, energy storage, and contaminant sorption in drinking water and wastewater. Given the high global demand for activated carbon products, scientists and industrialists are exploring the potential of biochar-derived biomass as precursors for activated carbons. This review presents and discusses the available studies on activated biochars produced from various precursor feedstocks and under different operating conditions in a two-step procedure: pyro-gasification (torrefaction, slow to flash pyrolysis, and gasification) followed by activation (physical, chemical or physicochemical). Findings from several case studies demonstrate that lignocellulosic residues provide attractive precursors, and that chemical activation of the derived biochars at high temperature and long residence time produces highly porous end materials. Indeed, the porosity of activated biochars varies greatly (from 200 to 2500 m2 g−1), depending on the pyro-gasification operating conditions and the feedstock (different feedstocks have distinct morphological and chemical structures). The results also indicate that the development of highly porous activated biochars for diverse purposes (e.g., electrodes for electrochemical energy storage devices, catalyst supports and adsorbents for water treatment) would benefit both the bioeconomy and the environment. Notably, it would leverage the potential of added-value biomass as an economical, non-fossil, readily available, and renewable energy source

Tannin Gels and Their Carbon Derivatives: A Review

International audienceTannins are one of the most natural, non-toxic, and highly reactive aromatic biomolecules classified as polyphenols. The reactive phenolic compounds present in their chemical structure can be an alternative precursor for the preparation of several polymeric materials for applications in distinct industries: adhesives and coatings, leather tanning, wood protection, wine manufacture, animal feed industries, and recently also in the production of new porous materials (i.e., foams and gels). Among these new polymeric materials synthesized with tannins, organic and carbon gels have shown remarkable textural and physicochemical properties. Thus, this review presents and discusses the available studies on organic and carbon gels produced from tannin feedstock and how their properties are related to the different operating conditions, hence causing their cross-linking reaction mechanisms. Moreover, the steps during tannin gels preparation, such as the gelation and curing processes (under normal or hydrothermal conditions), solvent extraction, and gel drying approaches (i.e., supercritical, subcritical, and freeze-drying) as well as the methods available for their carbonization (i.e., pyrolysis and activation) are presented and discussed. Findings from organic and carbon tannin gels features demonstrate that their physicochemical and textural properties can vary greatly depending on the synthesis parameters, drying conditions, and carbonization methods. Research is still ongoing on the improvement of tannin gels synthesis and properties, but the review evaluates the application of these highly porous materials in multidisciplinary areas of science and engineering, including thermal insulation, contaminant sorption in drinking water and wastewater, and electrochemistry. Finally, the substitution of phenolic materials (i.e., phenol and resorcinol) by tannin in the production of gels could be beneficial to both the bioeconomy and the environment due to its low-cost, bio-based, non-toxic, and non-carcinogenic characteristics

The influence of pilot-scale pyro-gasification and activation conditions on porosity development in activated biochars

Few studies have examined the influence of pyro-gasification and activation conditions on porosity development in activated biochars. In this context, this study investigates the effects of pyro-gasification temperature (315, 399, and 454 °C), activation temperature (700, 800, and 900 °C), and activating agent (CO2 flow rate: 2, 3, and 5 L min−1) on porosity in materials made from wood residues (black spruce and white birch). Activated biochars were prepared in a two-step process: torrefaction/fast pyrolysis in a pilot-scale plant and activation using an in-house pilot-scale furnace. Results show that the physical properties of activated biochars improved over biochars and wood residues, with fivefold greater surface area for activated birch biochar over biochars, and threefold greater surface area for activated spruce biochars. Statistical analysis results reveal that pyro-gasification and activation temperature, CO2 gas flow rate, and wood residue type significantly affected the porosity of activated biochars (at p < 0.05). The main findings are as follows: i) Torrefaction or pyrolysis pre-treatment step had less impact on the porosity of activated biochars, so lower energy expenditure is required to improve product quality, i.e., porosity; ii) Activation temperature was the major variable to optimize specific surface area; by increasing from 700 to 900 °C, the average surface area for activated biochars made from both wood residues increased to nearly 120 m2 g−1; iii) pilot-scale technologies produced porous activated biochars comparable to laboratory-scale technologies which could boost incentives to use thermochemical biomass conversion, and increase the profitability with these diversified by-products in biorefinery industry

Efficiency of eight modified materials for As(V) removal from synthetic and real mine effluents

Arsenic (As) contamination is a major problem especially for active gold mine operations. In the present study, eight low-cost materials including biochar (B), Fe-loaded biochar (BF), activated biochar (BC), Fe-loaded activated biochar (BCF and BFC), thermally modified dolomite (MD), wood ash (WA), and modified wood ash (MWA) were comparatively used for the efficiency in As(V) removal from synthetic and real mine effluents, through batch and column testing. Batch adsorption tests were conducted in beakers with a ratio adsorbent material and As(V) synthetic and real solutions of 0.1 g: 10 mL at concentrations of 850 and 300 µg/L As, respectively. Column adsorption tests were performed in 3 reactors with As(V) concentration of up to 900 µg/L in contaminated neutral drainage (CND) collected from a local gold mine. Results from batch testing with synthetic effluents showed the best performance for As(V) removal in the following order: MD > WA > BCF > BF > BFC > MWA > BC > B. Consistent findings were obtained in batch and column testing with the real mine effluent. Although iron grafted biochars are good adsorbents, their performance for As(V) removal was limited probably because of the very low As concentration in this study. In the same time, MD was found to be the most efficient material for As(V) removal but the final pH must be monitored and eventually adjusted. As(V) was completely removed by MD in batch testing (99.9%) and column testing (99.6%) after>112 days to bellow the authorized monthly mean allowed by Canadian discharge criteria. Thus, MD seems to be the most efficient material among the tested ones for the removal of As(V) in batch and column testing from synthetic and mine effluents

The conversion of wood residues, using pilot-scale technologies, into porous activated biochars for supercapacitors

In this study, activated biochar was produced using pilot-scale technologies of fast pyrolysis and activation to create desirable morphology, surface chemistry, and adsorptive properties for application in supercapacitors. First, residues from white birch were converted into biochar by fast pyrolysis (~ 450 °C). Then, physical (using CO2) or chemical (using KOH) activation was carried out in a homemade pilot-scale furnace at 900 °C. These synthesized materials presented distinct porosity structures: micro-/mesoporous (CO2 material) and highly microporous (KOH material), reaching surface areas of up to 1700 m2 g−1. Electrochemical results showed that KOH-activated biochar had higher specific electrical capacitance in both acidic and neutral electrolytes with a maximum specific capacitance value of 350 and 118 F g−1 at 1 A g−1, respectively; while, for CO2-activated biochar, the maximum obtained values were 204 and 14 F g−1. The greater proportion of oxygenated and nitrogenated functional groups on the surface of the KOH activated biochar, along with its high surface area (with wider porosity), improved its performance as a supercapacitor electrode. Specifically, the low proportion of ultramicropores was determinant for its better electrochemical behavior, especially in the neutral electrolyte. Indeed, these results are similar to those found in the literature on the electrical capacitance of carbonaceous materials synthesized in a small-scale furnace. Thus, the chemical-activated biochar made from wood residues in pilot-scale furnaces is a promising material for use as electrodes for supercapacitors