Physicochemical Properties Of Biochar Research Articles

Preparation and Modification of Biochar Materials and their Application in Soil Remediation

As a new functional material, biochar was usually prepared from biomass and solid wastes such as agricultural and forestry waste, sludge, livestock, and poultry manure. The wide application of biochar is due to its abilities to remove pollutants, remediate contaminated soil, and reduce greenhouse gas emissions. In this paper, the influence of preparation methods, process parameters, and modification methods on the physicochemical properties of biochar were discussed, as well as the mechanisms of biochar in the remediation of soil pollution. The biochar applications in soil remediation in the past years were summarized, such as the removal of heavy metals and persistent organic pollutants (POPs), and the improvement of soil quality. Finally, the potential risks of biochar application and the future research directions were analyzed.

Role of biochar and plant growth promoting rhizobacteria to enhance soil carbon sequestration-a review.

Global climate is undergoing significant changes due to extensive release of greenhouse gases (GHGs) such as CO2 and methane in the atmosphere. These gases are produced and released as a result of anthropogenic activities and fossil fuel burnings which also result in depletion of soil carbon resources. Biochar has various distinctive properties, which contribute to make it an effective, economical, and eco-friendly approach for soil carbon sequestration. The versatility in physicochemical properties of biochar provides an opportunity to optimize its efficacy to obtain desired benefits. A critical review of the literature indicates that biochar and plant growth-promoting microbes have the potential to improve soil organic carbon (SOC). Recent studies have depicted a significant role of the combined application of plant growth-promoting microbes and biochar on SOC dynamics. In future, these areas need to be explored as these have the potential to improve SOC dynamics and it could be a better strategy to sustain natural resources and ultimately mitigation of the climate change.

Cow manure-derived biochar: Its catalytic properties and influential factors.

The conversion of waste biomass into biochar is considered as a waste disposal alternative, especially because biochar is a low-cost adsorbent for soil contaminants. However, a risk of desorption of contaminants from biochar may lead to secondary pollution. This study investigated the degradation behavior of soil fumigant, 1,3-dichloropropne (1,3-D), on cow manure-derived biochar (CMB) pyrolyzed at five different temperatures from 300 to 700 °C (termed as C-300 to C-700). Results showed that 1,3-D degradation rate was U-shape related to biochar pyrolysis temperature. Four degradation byproducts (NH2CH2CH2CH3OH, CH3CH2NH2, NH2COCONH2, OHCH2COOH) were identified by headspace GC-MS. When biochar humidity improved from 0 to 50% or incubation temperature increased from 20 to 40 °C, the degradation of cis-1,3-D on C-300 improved 24.26% and 35.48%, respectively. The OH concentrations, detected by the terephthalic acid method, were considerably higher for C-300 than that for C-700. Pyrolysis temperature (300-700 ° C) governed biochar physicochemical properties and further affected 1,3-D degradation mechanisms (pH-controlled substitution or OH-restricted oxidation reaction). All these findings showed that CMB can adsorb and degrade 1,3-D, thereby reduce its desorption risk, indicative of the conversion of cow manure into biochar as an effective waste management practice.

S NUTRIENTS RTENTION OF SEVERAL BIOCHARS AND THEIR EFFECT ON N,P, K UPTAKE OF UPLAND-RICE .

ABSTRACT
 Application of biochar to agriculture soils has been considered as means to improve soil quality and carbon sequiestration. Therefore, the understanding of chemical and physical properties of biochars is important to identify suitable use of biochar for improving soil fertility and carbon sequestration. Biochars were produced from phyrolizing five different feedstock from crops residues (rice straw- BPJ, rice husk- BPS, maize cobs- BJT, peanuts shell- BKC and soybean residues-BKE). Using muffle furnace heating under 400oC. The potential nutrients retention of those biochars in particular for NH4+, K+. Ca++, dan Mg++. was tested. througha leaching experiment established in Soil Physic laboratory at Faculty of Agriculure, University of Mataram . The physicochemical properties of biochars were likely varied among fives feedstocks. The biochars derived from soybean residues (BKE), peanut biomass (BKC) and maize cobs (BJT) contained higher mutrients (i.e. C, N, K, Ca and Mg) compared to biochars produced from rice straw (BJP) and rice husks (BPS). Total-C of BKE, BKC dan BJT were 51,73; 57,36 dan 53,53 % respecively. The variation of phyisicochemical properties from different biomass strongly related to different nutrient retention whenever the biochars are applied in soils. Biochars produced from legume crops biomass such as soybean and dan peanuts werethe highest nutrients retention, followed by maize cobsand rice straw biochars. Unde glass house test, the tree biochars namely BPS, BJT and BKE have similar effect on N,P, K uptake as well as to dry weight biomass.

Lead removal from aqueous solutions using biochars derived from corn stover, orange peel, and pistachio shell

Biochar has been viewed as a cost-effective adsorptive material for heavy metals in water. In the present study, a total of nine different biochars synthesized from three different biomass types were studied: corn stover, organic peel, and pistachio shell at three pyrolysis temperatures (300, 450, and 600 °C). The efficiency of lead ion (Pb2+) removal by the biochars was investigated through batch adsorption experiments in parallel with physicochemical characterization of the biochars. Single-point Pb2+ adsorption at 10 mg L−1 showed that high-temperature corn stover biochar at 600 °C and low-temperature orange peel biochar at 300 °C performed the best in the Pb2+ removal (> 94%). Pistachio shell biochars were relatively poor at removing aqueous Pb2+ (20–35%). The efficiency of the Pb2+ removal increased with increasing pH (2–6) until a maximum adsorption of Pb2+ was observed at pH 6. Adsorption isotherms for Pb2+ were conducted using the best-performing biochars per biomass based on the single-point adsorption results. All isotherms were best described by the Langmuir model, and the Pb2+ sorption capacities were 25,000 mg kg−1 for corn stover biochar at 600 °C, 11,111 mg kg−1 for orange peel biochar at 300 °C, and 2500 mg kg−1 for pistachio shell at 600 °C. The physicochemical properties of biochars indicated that oxygen-containing functional groups and specific surface area were major parameters affecting aqueous Pb2+ removal. This study highlights that biomass type and pyrolysis temperature as well as solution pH are important in affecting the adsorption efficiency of Pb2+ from aqueous solution.

Influence of pH and grain size on physicochemical properties of biochar and released humic substances

The main goal of this study was to investigate the influence of pH and grain size of biochar on its physicochemical properties and on the quantity and quality of humic substances released from biochar. The studies were conducted on 5 biochar fractions and on the mixture of all fractions. Influence of grain size on physicochemical properties of biochar was characterized by analyzing changes in total carbon content, ash, density, total surface charge, average adsorption energy, specific surface area, content of functional groups and FTIR spectra. The effect of pH and grain size of biochar on releasing organic compounds were examined at pH of the extraction solution: 3, 5, 7 and 9 by analyzing aqueous extracts for changes in organic carbon content and for variation of humification degree coefficients. The results showed the grain size affected physicochemical properties of investigated material. The fraction <0.5 mm was characterized by the highest density, ash, content of functional groups and the lowest carbon content. Increasing grain diameter corresponded with decrease in average adsorption energy and with increase in the specific surface area. Only grain size, not pH of the solution, revealed clear effect on the quantity and quality of humic substances released from biochar.

Designing biochar properties through the blending of biomass feedstock with metals: Impact on oxyanions adsorption behavior

Metal-blending of biomass prior to pyrolysis is investigated in this work as a tool to modify biochar physico-chemical properties and its behavior as adsorbent. Six different compounds were used for metal-blending: AlCl3, Cu(OH)2, FeSO4, KCl, MgCl2 and Mg(OH)2. Pyrolysis experiments were performed at 400 and 700 °C and the characterization of biochar properties included: elemental composition, thermal stability, surface area and pore size distribution, Zeta potential, redox potential, chemical structure (with nuclear magnetic resonance) and adsorption behavior of arsenate, phosphate and nitrate. Metalblending strongly affected biochars' surface charge and redox potential. Moreover, it increased biochars' microporosity (per mass of organic carbon). For most biochars, mesoporosity was also increased. The adsorption behavior was enhanced for all metal-blended biochars, although with significant differences across species: Mg(OH)2-blended biochar produced at 400 °C showed the highest phosphate adsorption capacity (Langmuir Qmax approx. 250 mg g−1), while AlCl3-blended biochar produced also at 400 °C showed the highest arsenate adsorption (Langmuir Qmax approx. 14 mg g−1). Significant differences were present, even for the same biochar, with respect to the investigated oxyanions. This indicates that biochar properties need to be optimized for each application, but also that this optimization can be achieved with tools such as metal-blending. These results constitute a significant contribution towards the production of designer biochars.

A comprehensive review on physical activation of biochar for energy and environmental applications

AbstractBiochar is a solid by-product of thermochemical conversion of biomass to bio-oil and syngas. It has a carbonaceous skeleton, a small amount of heteroatom functional groups, mineral matter, and water. Biochar’s unique physicochemical structures lead to many valuable properties of important technological applications, including its sorption capacity. Indeed, biochar’s wide range of applications include carbon sequestration, reduction in greenhouse gas emissions, waste management, renewable energy generation, soil amendment, and environmental remediation. Aside from these applications, new scientific insights and technological concepts have continued to emerge in the last decade. Consequently, a systematic update of current knowledge regarding the complex nature of biochar, the scientific and technological impacts, and operational costs of different activation strategies are highly desirable for transforming biochar applications into industrial scales. This communication presents a comprehensive review of physical activation/modification strategies and their effects on the physicochemical properties of biochar and its applications in environment-related fields. Physical activation applied to the activation of biochar is discussed under three different categories: I) gaseous modification by steam, carbon dioxide, air, or ozone; II) thermal modification by conventional heating and microwave irradiation; and III) recently developed modification methods using ultrasound waves, plasma, and electrochemical methods. The activation results are discussed in terms of different physicochemical properties of biochar, such as surface area; micropore, mesopore, and total pore volume; surface functionality; burn-off; ash content; organic compound content; polarity; and aromaticity index. Due to the rapid increase in the application of biochar as adsorbents, the synergistic and antagonistic effects of activation processes on the desired application are also covered.

Upgrading biochar from bio-oil distillation residue by adding bituminous coal: Effects of induction conditions on physicochemical properties

In this study, biochar was produced by co-pyrolysis of bio-oil distillation residue and bituminous coal under different induction temperature and gas flow rate in a tube furnace. Central composite design was introduced to explore the combined effects of experimental conditions on biochar. The physicochemical properties of biochar from different induction conditions were comprehensively evaluated by elemental analysis, Fourier transform infrared spectrometry (FTIR) and Raman spectroscopy based on response surface methodology. The results showed that bituminous coal was beneficial to the increase in biochar yield, whereas temperature had the opposite effect and the effect of gas flow rate was not obvious. Moreover, C/O ratio increased with the increase of pyrolysis temperature and bio-oil distillation residue in feedstocks, while C/H ratio increased only with increasing temperature. Gas flow rate had a more pronounced descent effect on C/H compared with C/O. In addition, induction conditions caused a relative weakening of CC stretching vibration and the relative enrichment of CH in biochar. Bituminous coal, temperature and gas flow rate all contributed to the conversion of small aromatic rings of biochar to large aromatic rings during the co-pyrolysis process.

Suitability of Different Agricultural and Urban Organic Wastes as Feedstocks for the Production of Biochar—Part 1: Physicochemical Characterisation

Biochar is traditionally made from clean lignocellulosic or waste materials that create no competition for land use. In this paper, the suitability of alternative feedstocks of agricultural and urban origins are explored. A range of biochars was produced from holm oak and a selection of organic wastes, such as greenhouse wastes, greenwastes, a cellulosic urban waste, municipal press cake and pig manure. They were characterized and assessed for their potential agricultural use. The physicochemical properties of biochars were mainly driven by the characteristics of feedstocks and the pyrolysis temperature. The use of pre-treated lignocellulosic residues led to biochars with a high concentration of ash, macro and micronutrients, whereas raw lignocellulosic residues produced biochars with characteristics similar to traditional wood biochars. All biochars were found to be suitable for agricultural use according to the international standards for the use of biochars as soil amendments, with the exception of a biochar from urban origin, which presented high levels of Cr and Pb. The use of these biochars as soil amendments requires a thorough agronomical evaluation to assess their impact on soil biogeochemical cycles and plant growth.

Covalent immobilization of laccase on citric acid functionalized micro-biochars derived from different feedstock and removal of diclofenac

Immobilization of enzymes on the solid supports can improve the stability as well as catalytic properties of enzymes. In this study, biochar derived from various feedstocks were used as immobilization support considering biochars carbon negative as well as sustainable properties. Partially purified (concentrated) crude laccase was covalently immobilized onto pine wood (BC-PW), pig manure (BC-PM) and almond shell (BC-AS) micro-biochars using optimized 5% w/v glutaraldehyde. Moreover, citric acid pretreatment improved the laccase binding capacity of all the micro-biochars and the highest laccase binding of 40.2 ± 1.8 U g−1 was observed with BC-PM in comparison with raw BC-PM (34.1 ± 1.1 U g−1). The enhanced binding of laccase on BC-PM over wood derived biochars was attributed to the higher surface area (46.1 m2 g−1) of BC-PM. Moreover, feedstock selection as well as a method of production influenced the biochar physicochemical properties such as surface area and consequently, different biochars showed various laccase immobilization efficiencies. BC-PW showed better pH, thermal, storage, and operational stability, compared with BC-AS and BC-PM. While applying the laccase bound micro-biochar, complete removal was observed in 2 h under batch mode with 0.5 g of laccase bound BC-PM at an environmentally relevant concentration of 500 µg L−1 in wastewater effluent. About 40% of the laccase activity was retained with all the laccase-bound micro-biochars after 5 cycles of diclofenac treatment.

Cadmium adsorption by biochar prepared from pyrolysis of silk waste at different temperatures

In this study, biochars (BC300, BC500 and BC700) were produced from silk waste through pyrolysis under oxygen-limited condition at 300, 500 and 700 ℃, respectively. The physicochemical properties of biochar were detected by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffractometer (XRD) and specific surface area analyzer. The Cd2+ adsorption capacities of biochars were investigated. Results showed that BET surface area, pH, and ash were increased with the increases of pyrolysis temperature. SEM images showed that the surfaces of biochars were rough and irregular. XRD and FT-IR results showed that all the silk waste biochars obtained at different temperatures contained calcite. pH had limited influence on the removal efficiency of biochar for Cd2+. Langmuir isotherm fitted the experimental data quite well. The Langmuir monolayer adsorption capacity of BC300, BC500, and BC700 were 25.61, 52.41, and 91.07 mg·g-1, respectively. The adsorption of Cd2+ onto the biochars obeyed a pseudo second-order kinetic model, with the BC700 showing the best removal efficiency. Further-more, the effects of the ionic strength and coexisting cations on Cd2+ removal were investigated. The results showed that the removal of Cd2+ was decreased with the increases of NaCl. Among the coexisting cations, the removal of Cd2+ was decreased by Ca2+ and Mg2+, while K+ had limited effect on the removal of Cd2+. In conclusion, the biochar derived from silk waste pyrolysis is a potential attractive adsorbent for the removal of Cd2+ from water.

Metal(loid) immobilization in soils with biochars pyrolyzed in N2 and CO2 environments

Previous studies indicated that using CO2 as a reaction agent in the pyrolysis of biomass led to an enhanced generation of syngas via direct reaction between volatile organic carbons (VOCs) evolved from the thermal degradation of biomass and CO2. In addition, the physico-chemical properties of biochar in CO2 were modified. In this current study, biochars generated from red pepper stalks in N2 and CO2 (RPS-N and RPS-C, respectively) were tested for their effects on the immobilization of Pb, Cd, Zn, and As in contaminated soils. Soils were incubated for one month with 2.5% of RPS, and two biochars (i.e., RPS-N and RPS-C) at 25°C. After the incubation period soils were analyzed to determine the amendment effects on the behavior of metal(loid)s. The potential availability and mobility kinetics of metal(loid)s were assessed by single extraction of ammonium acetate and consecutive extraction of calcium chloride, respectively. Sequential extraction was used to further examine potential changes in geochemical fractions of metal(loid)s. The increased soil pH induced by application of the biochars reduced the potentially available Pb, Cd, and Zn, while RPS-C significantly reduced Pb due to the high surface area and aromaticity of RPS-C. However, RPS-C mobilized potentially available As compared to RPS-N due to the increased soil pH. Biochars reduced the mobility kinetics of Pb, Cd, and Zn, and RPS-N effectuated the greatest reduction of As mobility. The RPS-C increased the Fe and Mn oxides, hydroxide, and organically bound Pb, while both biochars and RPS-N increased residual Cd and Zn, and organically bound As, respectively. When considering the two biochars, RPS-C was highly effective for immobilization of Pb in soils, but it had no effect on Cd and Zn and a negative effect on As. In addition, RPS-C significantly increased the total exchangeable cations in soils.

Improvement and maintenance of biochar catalytic activity for in-situ biomass tar reforming during pyrolysis and H2O/CO2 gasification

To study the role of gasifying agents (H2O/CO2) on the improvement and maintenance of biochar catalytic activity for in situ biomass tar reforming, experiments were carried out in a two-stage fluidized-bed/fixed-bed reactor. The physicochemical properties of biochar, which are responsible for its catalytic activity during tar reforming, were analyzed by ICP–AES, SEM–EDX, BET and XPS methods. The conversion of biomass tar was investigated by GC–MS. Adding H2O or CO2 was found to improve the homogeneous and heterogeneous reforming of biomass tar, the latter of which involved first forming an intermediary coke product that was subsequently gasified by H2O/CO2. Activation of biochar by H2O/CO2 impacted the biochar surface's morphology and distribution of metal species. During tar reforming, the presence of H2O/CO2 also affected the creation and regeneration of pore structures, influencing the biochar's structure and dynamically distributing AAEM species, which ensured enough surface active sites to maintain the biochar's catalytic activity. CO2 produced more micropores in the biochar, whereas H2O favored the formation of mesopores, which are more important for tar reforming. The addition of H2O/CO2 was found to notably enhance in situ reforming of both large and small aromatic ring systems in biomass tar over biochar.

A novel pyro-hydrochar via sequential carbonization of biomass waste: Preparation, characterization and adsorption capacity

Comprehensive utilization of agricultural biomass waste, such as biochar, is a hot spot in recent years. In order to keep high chemical stability, large specific surface area, and rich oxygenated functional groups of carbonized product, a novel rich-carbon material ‘pyro-hydrochar’ was proposed firstly via sequential carbonization of biomass wastes. In the present study, the pyro-hydrochar was derived from the corn straw and corncob by consecutive hydrothermal carbonization under 200 °C and then pyrolysis at the temperatures of 350–650 °C. The physicochemical properties of biochar, hydrochar and pyro-hydrochar were compared by multi-analysis including the characterization by elemental composition, BET, FTIR, XPS, SEM, chemical oxidation method by K2Cr2O7 and H2O2. The results showed the pyro-hydrochar is a newly developed rich carbon material with large specific surface area, rich functional groups, high aromatization degree and strong chemical oxidation stability. Specifically, the stable carbon-rich pyro-hydrochar indicates the strong capacity of potential carbon sequestration. Additionally, the biochar, hydrochar and pyro-hydrochar could show different adsorption performance on the representative contaminants like atrazine, Cd2+ and Cr(VI). It suggested the pyro-hydrochar with rich oxygenated functional groups and large specific surface area could be a new candidate of economic adsorbent, and it also indicated the important practical value for further modification and development of pyro-hydrochar derived from biomass wastes.

Influence of sodium dodecyl sulfate coating on adsorption of methylene blue by biochar from aqueous solution

Biochar is regarded as a promising new class of materials due to its multifunctional character and the possibility of effectively coupling different properties. With increasing introduction into the environment, environmental chemicals such as surfactants will load onto the released biochar and change its physicochemical characteristics and adsorption behavior toward pollutants. In this study, sodium dodecyl sulfate (SDS), as one type of anionic surfactant, was coated onto biochar with different loading amounts. The influence of SDS loading onto biochar's physicochemical properties were investigated by Fourier transform infrared (FT-IR) spectroscopy, elemental analysis, zeta potential and Brunauer–Emmett–Teller (BET) surface area and pore size distribution analysis. Results showed that the pore size of the biochar decreased gradually with the increase of SDS loading because of the surface-adsorption and pore-blocking processes; the pH of the point of zero charge (pHPZC) decreased with increasing SDS loading. Although surface-coating with SDS decreased the pore size of the biochar, its adsorption capacity toward Methylene Blue (MB) significantly increased. The biochar-bound SDS introduced functional groups and negative charges to the biochar surface, which could thus enhance the adsorption of MB via hydrogen bonding and electrostatic interaction. The results can shed light on the underlying mechanism of the influence of anionic surfactants on the adsorption of MB by biochar.

Site energy distribution analysis and influence of Fe3O4 nanoparticles on sulfamethoxazole sorption in aqueous solution by magnetic pine sawdust biochar

Magnetisation of carbonaceous adsorbents using iron oxides has been found to be one of the potential solutions for easy recovery of adsorbent after use. We evaluated the effects of Fe3O4 nanoparticle addition on the physico-chemical properties of biochar and its sorption properties. Five adsorbents with varying amount of Fe3O4 per mass of adsorbent (0%, 25%, 50%, 75% and 100%) were used to adsorb sulfamethoxazole (SMX), an emerging micropollutant. Five isotherm models were used to evaluate the sorption behaviour of SMX onto the adsorbents where Redlich-Peterson model was found to best describe the data. Based on this model, the approximate site energy distribution for each adsorbent was determined. Surface area and sorption capacity had strong negative linear relationship with the amount of Fe3O4 per mass of adsorbent while the pore volume and saturation magnetisation of the adsorbent increased with increasing percentage of Fe3O4. The results of the approximate site energy distribution analysis showed that the addition of Fe3O4 on biochar reduced the area under the frequency distribution curve of sorption site energies leading to the lowering of the sorption sites available for SMX. This could be attributed to the blockage of the hydrophobic surface of biochar reducing the hydrophobic interaction between SMX and biochar.

Correlations and adsorption mechanisms of aromatic compounds on biochars produced from various biomass at 700°C.

Knowledge of adsorption behavior of organic contaminants on high heat temperature treated biochars is essential for application of biochars as adsorbents in wastewater treatment and soil remediation. In this study, isotherms of 25 aromatic compounds adsorption on biochars pyrolyzed at 700°C from biomass including wood chips, rice straw, bamboo chips, cellulose, lignin and chitin were investigated to establish correlations between adsorption behavior and physicochemical properties of biochars. Isotherms were well fitted by Polanyi theory-based Dubinin-Ashtakhov (DA) model with three parameters, i.e., adsorption capacity (Q0) and adsorption affinity (E and b). Besides the negative correlation of Q0 with molecular maximum cross-sectional areas (σ) of organic compounds, positive correlations of Q0 with total pore volume (Vtotal) and average diameter of micropore (D) of biochars were observed, indicating that adsorption by biochars is captured by the pore-filling mechanism with molecular sieving effect in biochar pores. Linear solvation energy relationships (LSERs) of adsorption affinity (E) with solvatochromic parameters of organic compounds (i. e., αm and π∗) were established, suggesting that hydrophobic effect, π-π interaction and hydrogen-bonding interaction are the main forces responsible for adsorption. The regression coefficient (π1) and intercept (C) of obtained LSERs are correlated with biochar H/C and Rmicro, respectively, implying that biochars with higher aromaticity and more micropores have stronger π-π bonding potential and hydrophobic effect potential with aromatic molecule, respectively. However, hydrogen-bonding potential of biochars for organic molecules is not changed significantly with properties of biochars. A negative correlation of b with biochar H/C is also obtained. These correlations could be used to predict the adsorption behavior of organic compounds on high heat temperature treated biochars from various biomass for the application of biochars as sorbents and for the estimating of environmental risks of organic compounds in the present of biochars.

Adsorption Characteristics of Biochar on Heavy Metals (Pb and Zn) in Soil

Three types of biochars, poplar branch biochar (PBC), water hyacinth biochar (WHC), and corn straw biochar (CSC), were prepared in a fixed-bed pyrolyzer at different pyrolysis temperatures (300-700℃). The effects of biochar species, pyrolysis temperature, and biochar addition on adsorption characteristics of typical heavy metals (HMs) such as Pb and Zn in vegetable soil (collected from a lead-zinc-silver mining area, Nanjing, China) were investigated. The adsorption mechanism of biochar on HMs was discussed based on the analyses of pore structure, XRD, and FTIR of biochars. WHC biochar showed the best adsorption ability at the same experimental conditions with adsorption efficiencies on Zn and Pb of 21.83% and 44.57%, respectively. The relative adsorption capacities of Zn and Pb were 227.65 μg·g-1 and 363.76 μg·g-1 at the pyrolysis temperature of 500℃ and biochar addition of 5%. The adsorption efficiency of biochar on HMs in soil increased gradually with increasing pyrolysis temperature. WHC biochars prepared at 500℃ and 700℃ had similar adsorption capacities on Zn and Pb in soil indicating that the moderate pyrolysis may be a good choice for WHC with better physicochemical properties. Increasing the amount of WHC addition benefits the adsorption efficiency of HMs in soil, but does not increase the adsorption capacity. The adsorption efficiency of Pb in soil reaches 93.93% by adding 10% of WHC into the soil sample. The combined analyses based on the physicochemical properties of biochar and the results of soil HMs adsorption experiments suggest that ion exchange and complexation are prevailing mechanisms of the remediation of HM-contaminated soil by WHC biochars.

Morphological and physicochemical characterization of biochar produced by gasification of selected forestry species

In this study, biochar samples acquired as by-product by downdraft gasification at 700 °C from Eucalyptus grandis (BC-EG), Acacia magnium (BC-AM) and Gmelina arborea (BC-GA) were characterized. The morphological characteristics and physicochemical properties of biochar were studied using nitrogen physisorption by the Brunauer-Emmet-Teller (BET) method, Scanning Electron Microscopy (SEM), X-ray Energy Dispersive Spectrometry (EDX) and Fourier Transform Infrared Spectroscopy (FTIR). The surface area (SA) of the materials was in the 2.0-50.0 m2/g range, with the biochar obtained from BC-EG showing the highest SA (50.0 m2/g), while the biochar derived from BC-GA showed the lowest SA (2.0 m2/g). In addition, all samples can be classified as mesoporous materials because their pore sizes were between 2 and 50 nm. This indicates that these materials can be used in absorption processes; however, the biochar obtained from BC-AM is expected to be the most suitable for absorption applications. FTIR biochar spectra did not exhibit characteristic peaks for cellulose or hemicellulose in any sample due to decomposition of these compounds at the gasification temperature. Moreover, according to SEM/EDX analyzes, all the samples presented well-defined pore structure and contained minerals as Na, K and Ca, suggesting that the biochar could also be useful for soil amendment applications.