Char Content Research Articles

Evolution and speciation transformation of chlorine during automobile shredder residue pyrolysis

Disposal of automobile shredder residue (ASR) via pyrolysis enables the recovery of valuable products; however, the production of hazardous pollutants and low-value products is inevitable due to its high chlorine content. In this work, chlorine evolution behavior and the conversion mechanism during ASR pyrolysis between 480 and 600 °C were systematically studied. The experimental results for organic chlorine (Org-Cl) showed that released chlorinated gases were complex, and HCl only accounted for 35% of the gas phase products, while short-chain hydrocarbons with carbon atoms between two and four accounted for 52%. Chlorine was predominantly retained in the char, and Org-Cl was the primary contributor to the residual chlorine, accounting for over 50% of the char. The content of inorganic chlorine (InO-Cl) was low in the raw sample but significantly increased in the char. Through the distinction between organic and inorganic chlorine content in char, it was confirmed that Org-Cl could be converted to InO-Cl due to complex secondary reactions with metallic compounds. The conversion was favored by increasing the Org-Cl content and the temperature. Our findings clarified the evolution mechanism of chlorine and the transformation from Org-Cl to InO-Cl, thus providing guidance for chlorine regulation and the efficient recycling of metal resources.

Synergistic effects and product yields in microwave-assisted in-situ co-pyrolysis of rice straw and paraffin wax

Microwave-assisted pyrolysis is one of the most efficient methods for solid waste management. This study employed microwave-assisted catalytic co-pyrolysis to convert Paraffin wax (PW) and rice straw (RS) into valuable char, gas, and oil products. KOH and graphite were used as the catalyst and susceptor, respectively. The RS and PW blend served as the feedstock (with a blend ratio of 0–10 g). The yields of co-pyrolysis at different blending ratios of RS: PW exhibited variations in char content (ranging from 9.8% to 22.6% by wt.), oil production (ranging from 34.1% to 76.9% by wt.), and gas formation (ranging from 13.2% to 47.5% by wt.). The effects of the RS: PW ratio on the average heating rate, feedstock conversion, and product yields were also investigated. Analyses were performed to assess the synergistic impacts on product yields, average heating rates, and conversion factors. Notably, co-pyrolysis synergy led to increased oil and char production. Furthermore, we conducted FTIR analysis on the oil and char produced through the catalytic co-pyrolysis of RS: PW. In conjunction with co-pyrolysis synergy, the catalyst facilitated the formation of amides, alkenes, aliphatic compounds, and aromatic compounds.

Microwave-Assisted Chemical Purification and Ultrasonication for Extraction of Nano-Fibrillated Cellulose from Potato Peel Waste

Nanofibrillated cellulose was extracted from potato peel waste using a fast and green method with a simple process. To extract cellulose and eliminate non-cellulosic constituents, alkaline and hydrogen peroxide treatments were performed under microwave irradiation. The nanofibrillated cellulose was extracted from purified cellulose via TEMPO oxidation followed by ultrasonication. The TEM, FTIR, XRD, and TGA experiments were used to evaluate the structural, crystalline, and thermal properties of cellulose fiber and nanofiber. The chemical and FTIR analysis of bleached fibers indicates that almost all non-cellulosic components of biomass have been eliminated. The diameter of the extracted nanofibers is in the range of 4 to 22 nm. In terms of crystallinity, extracted nanocellulose had 70% crystallinity, compared to 17% for unprocessed lignocellulose fibers, which makes it an excellent choice for use as a reinforcement phase in biobased composites. Thermogravimetric analysis reveals that cellulose nanofibers are less thermally stable than potato peel pure cellulose, but it has a higher char content (28%) than pure cellulose (6%), which signifies that the carboxylate functionality acts as a flame retardant. The comparison between cellulose derived from microwave and conventional extraction methods confirmed that their impact on the removal of non-cellulosic materials is nearly identical.

Influence of pyrolysis atmosphere, temperature, and particle size co-regulation on the physicochemical properties of bone char

Compared to other biochars, bone char can take advantage of its unique mesoporous structure and ionic polarity sites for adsorption. However, previous studies have not clarified the influence of various process parameters on the physicochemical properties of bone char. Therefore, we systematically analyzed the physicochemical properties of bone char with different pyrolysis atmospheres (CO2/N2), temperatures (300–900 °C), and particle sizes (less than 0.15 mm, 0.15–0.45 mm, and 0.45–0.90 mm) and their differences. The results showed that the pyrolysis atmosphere at 900 °C significantly affects the physicochemical properties of bone char, such as pore structure, ash content, electrical conductivity, surface functional groups, and crystal structure. The pyrolysis temperature is crucial in regulating the pore structure, ash content, acidity, and other physicochemical properties of bone char. It plays a significant role in the pyrolysis process from 300 °C to 500 °C and from 700 °C to 900 °C. The particle sizes significantly affect the electrical conductivity and basic functional group content of bone char at different pyrolysis atmospheres and temperatures. The bone char with sizes less than 0.15 mm prepared at 700 °C with N2 as the pyrolysis atmosphere has a rich mesoporous structure, a higher ash content, a higher basic functional group content, etc., and is more suitable as an adsorbent. The study results provide a theoretical basis for selecting appropriate pyrolysis process parameters to produce bone char that meets environmental treatment applications.

Temperature effect on density, strength, and microstructure of sustainable coal char-cement grout

Coal char, a coal pyrolysis product, is a lightweight carbon-rich material, which exhibits significant potential as an innovative and sustainable construction material. Recent research has indicated that the coal char addition enhances the engineering performance of conventional cement grout at ambient temperature. This experimental study evaluates the performance of coal char-cement grouts under varying curing temperatures (−25, 5, 25, and 35 °C) and conditions (sealed and water-soaked), focusing on the impacts of char contents (≤30 %) and temperatures on the bulk density, unconfined compressive strength, mineralogical, and microstructural properties of grouts. Findings reveal that grouts cured at 5, 25, and 35 °C possess 7.0–7.9 %, 5.3–5.4 %, and 5.1–6.4 % higher bulk density than those cured at −25 °C, primarily attributable to water absorption in water-soaked curing conditions. Furthermore, at −25 °C, the increasing compressive strength is obtained in low w/c ratio (0.8) grouts as char content increases. Compared to curing temperatures of 5 and 35 °C, char-cement grout at an ambient temperature of 25 °C demonstrates better strength performance because of more hydration products formed, higher calcite content, the predominance of amorphous calcium silicate hydrate, and the reduction in the crystalline phase of portlandite.

New coal char-based bricks: Effects of curing temperature, humidity, pressing pressure, and addition of superplasticizer on the physical, mechanical, and thermal properties

Coal char, as a sustainable and eco-friendly material, holds significant potential for use in new construction materials, specifically, coal char-based bricks. This study employed the pre-pressing method to create char bricks containing high char content of 70%. The impact of various curing temperatures (20, 40, 60 °C), humidity levels (15% and 90%), and pressing pressures (3.5, 7, and 10 MPa) on the density, X-ray diffraction, compressive strength, and thermal conductivity of char-based samples were examined. The addition of superplasticizer and the performance of char bricks were assessed by comparing them to traditional clay bricks and corresponding standards. The study discovers that the temperature of 40 °C enhances the early 7-day strength of char brick samples, while the highest 28-day strength is observed in char bricks at a temperature of 20 °C and humidity of 90%. Compared to conventional clay bricks (with density of 1.9 g/cm3, thermal conductivity of 0.39–0.63 W/mK, compressive strength of 10–20 MPa), the proposed char bricks exhibit lower density (∼0.8 g/cm3), lower thermal conductivity (0.26–0.35 W/mK), and good performance in compressive strength (up to 15 MPa). In conclusion, coal char-based bricks with high char content demonstrate significant advantages over traditional clay bricks, making them a sustainable and environmentally friendly building material option.

Comprehensive insight into co-pyrolysis of sewage sludge and tobacco stalk: Effects of mixing ratio and pyrolysis conditions on product distribution and characteristics

Co-pyrolysis of sewage sludge (SS) and tobacco stalk (TS) was conducted, where TS are rich in inorganic elements. The effects of the mixing ratio and pyrolysis temperature on pyrolysis products were investigated through the tube furnace system. The components of gas and tar were determined. In addition, the N/S ratio, pore distribution characteristics, surface functional group characteristics, aromatisation characteristics and inorganic element content of char were studied. Results show that the addition of TS to SS has a significant synergistic effect. Particularly, when the ratio of SS to TS is 1:3, the pyrolysis gas yield is the largest. The inorganic elements with a catalytic effect can promote the conversion of char and tar into pyrolysis gas. However, with the increase in pyrolysis temperature, the synergistic effect will gradually weaken. The increase in pyrolysis temperature will promote the development of mesopores in char but will reduce the order degree of the char structure. The addition of TS in SS will further increase the number of mesopores in char, and the obtained char carbon structure is more ordered. When the pyrolysis temperature is 600 °C, the tar yield is the highest, and the higher the mixing ratio of SS, the better the formation of polyaromatic compounds and aliphatic hydrocarbons.

Pyrolysis magnetization of low-rank coal and distribution characteristics of sulfur and heavy metals in char products

The distribution of sulfur and heavy metals in char of Gansu lignite and Shanxi subbituminous coal was studied by means of pyrolysis and magnetic separation at different pyrolysis temperatures. The contents of sulfur and heavy metal elements in char were analyzed and determined by ICP-OES and ICP-MS, and the mineral composition and apparent morphology of char were characterized by XRD and SEM-EDS. The results show that the highest desulfurization rates of Gansu lignite and Shanxi Subbituminous coal can reach 52.37% and 17.54% respectively under optimal conditions. This is related to the phase transition behavior of pyrite during pyrolysis. The desulphurization rate of Shanxi subbituminous char is lower than that of Gansu lignite char mainly because the occurrence and inclusion of associated minerals and the organic matter influence the transformation of pyrite during pyrolysis. Ni and Cr have a strong affinity with Fe−S minerals, which are enriched into magnetic char with sulfur. At 800 °C, Cr content in magnetic char of Gansu coal and Shanxi coal is 8698.25 and 32327.47 μg/g higher than that in non-magnetic char, respectively. The pyrolytic magnetization of low-rank coal and the distribution of sulfur and heavy metals in its char products provide data support and a new idea for removal of sulfur and heavy metals from coal.

Development of high-strength and durable coal char-based building bricks

Pyrolysis coal char is a byproduct of the coal industry and causes undesirable environmental issues from conventional coal combustion and gasification. This paper presents a novel approach to utilize coal char for manufacturing new and environmentally friendly building bricks. The effects of sand, silica fume (SF), superplasticizer (SP), air-entraining admixture (AE), and graphene oxide (GO) on the properties of char-based bricks, including heat of hydration, thermogravimetric and differential thermal analysis, microstructures, density, and compressive strength, are investigated. A new treatment method using hydrophobic liquid in a vacuum condition is proposed to improve the durability of char bricks, which is evaluated based on water absorption and freeze-thaw (F-T) cycles. The experimental results indicate that the new bricks with 40% char content have a good compressive strength performance of 49.2–52.5 MPa, which compares favorably to conventional clay bricks with compressive strength of 10–20 MPa. Adding AE and GO slightly increases and decreases the compressive strength at 28 days, respectively. Moreover, the proposed treatment method significantly improves the durability of char bricks. The treated char bricks exhibit a boiling water absorption of ≤2.3%, which is 90% lower than that of untreated char bricks. The untreated and treated char bricks can achieve 22 and 120 F-T cycles, respectively. Overall, this study presents a promising approach to repurpose coal char and produce sustainable building bricks with high compressive strength and durability.

Comparative study of continuous and batch microwave-assisted pyrolysis of waste printed circuit boards: product characteristic, bromine transformation, and energy efficiency assessment

To realize the efficient processing and resource utilization of waste printed circuit boards (WPCBs), products characteristics, pollutants control, and energy conversion between batch microwave-assisted pyrolysis (BMAP) and continuous microwave-assisted pyrolysis (CMAP) were compared and analyzed. CMAP promoted decomposition of oxygenated and Br/N-containing compounds in char, producing char with stronger aromatization and graphitization. CMAP facilitated bromine fixation in char, with higher bromine yield in solid product and lower bromine yield in condensate (71.69 and 18.80 wt %, respectively) than BMAP (67.51 and 29.11 wt %, respectively). For catalytic CMAP, continuous mixing promoted heat exchange between WPCBs and hot K2CO3 particles thus providing a higher heating rate, which led to a higher condensate yield than BMAP. K2CO3 promoted >95% of bromine retained in char during both processes. The higher KBr content in char, and lower concentrations of Br-containing compounds in pyrolysis oil and lower HBr yield were achieved from catalytic CMAP compared to BMAP, mainly due to more uniformly mixing of solid and volatiles in CMAP process. CMAP had more supremacy than BMAP in significantly enhancing energy efficiency. The results provide theoretical basis for the green utilization of WPCBs and development of microwave pyrolysis from batch to continuous modes.

Synergetic modification of graphitic carbon nitride by Zr-based metal-organic framework and tetraethoxysilane for improving fire performance in composite coatings

In this study, in an attempt to get an excellent flame retardant, herein, a new nanofiller (CNP@UiO-66@TEOS) with polyethyleneimine (PEI) as a crosslinker, Zr-based metal-organic framework (UiO-66) and tetraethoxysilane (TEOS) modified graphitic carbon nitride (CN) was synthesized. Different characterization tests confirmed the successful preparation of CNP@UiO-66@TEOS. Then, CNP@UiO-66@TEOS was doped into intumescent fire retardant (IFR) coating by solution blending method and the coating (CNP@UiO-66@TEOS/EP) was gained after curing. As expected, the CNP@UiO-66@TEOS significantly improved the fire performance of the IFR coating. The coating (CNP@UiO-66@TEOS/EP) with the addition of 2 wt% CNP@UiO-66@TEOS reduced the backside temperature by 102.9 °C over that of pure EP, proving enhanced flame retardancy. Meanwhile, CNP@UiO-66@TEOS/EP achieved the highest expansion height (21.5 mm) in the furnace experiment, contributing to a lower heat transfer ratio. In addition, the thermogravimetric analysis revealed an increase in residual char content to 31.84 wt%, which helped to resist external heat penetration. Cone calorimeter testing (CCT) showed that the peak heat release rate (PHRR), total heat release rate (THR), peak smoke production rate (PSPR), total smoke production (TSP), peak CO production rate (PCOPR), and peak CO2 production rate (PCO2PR) of CNP@UiO-66@TEOS/EP were reduced by 29 %, 19 %, 35 %, 37 %, 36 %, and 19 %, respectively, compared to pure EP, demonstrating the improved flame retardancy and smoke suppression properties. The results indicated that CN formed a thermal barrier at a high temperature and UiO-66 generated zirconium oxide (ZrO2) to catalyze the formation of residual char, thus producing a barrier effect. The TEOS on the UiO-66 surface further decomposed to form a silicon network to enhance the char layer strength of the composite. The synergistic outcome of CN, UiO-66, and TEOS offers potential avenues for the development of efficient IFR coating.

Gasification behavior and kinetics of chars derived from coal pyrolysis in a CO-containing atmosphere

Char gasification enables clean and efficient utilization of low-rank coal resources. The CO2 gasification behavior and kinetics of char samples produced via low-rank coal pyrolysis under the N2 and CO-containing atmospheres (char-N2 and char-CO) were investigated based on a series of thermogravimetric experiments, and the physicochemical structure of chars were characterized via Raman diffraction, X-ray diffraction, and CO2 adsorption methods, respectively. The apparent activation energies (Ea) of char-N2 and char-CO were obtained using the Flynn–Wall–Ozawa method and the reaction mechanism was determined via the Malek method. The results indicate that the graphitization and order degrees of the carbon chemical structure of char-CO are higher than those of char-N2 below gasification temperature (approximately 850 °C), whereas the specific surface area of char-CO is higher than that of char-N2 before gasification. Char-CO gasifies faster than char-N2 owing to its developed pore structure, and the gasification activation energy is lower than that of char-N2 (from 450 °C to 650 °C, the activation energy of char-N2 is 186.3 kJ mol−1, 192.4 kJ mol−1, and 203.6 kJ mol−1, and that of char-CO is 175.8 kJ mol−1, 187.5 kJ mol−1, and 199.1 kJ mol−1, respectively). The CO2 gasification reaction process of char-N2 and char-CO can be explained using a three-dimensional diffusion model. Moreover, the ash content in coal char affects the diffusion of reaction carrier gas and gas products during the gasification process, indicating that diffusion is the primary limiting factor in coal char CO2 gasification.

Pyrolysis of mixed plastic fractions – Development of predictive models for yield and oil quality

Pyrolysis of plastic mixtures has shown to form complex mixtures of oil, which is difficult to predict. Interaction effects between plastics have shown to affect both the oil composition and the yield distribution of oil, char, and gas. This work aims to generate models for the prediction of oil and char yield, acid number, and viscosity based on the feed composition. Besides the oil composition based on the reactor feed was mapped. Pyrolysis was performed in a batch reactor with a mixture of PP, PE, EVA, PET, PS and PA, where the content of PET, PS and PA were varied from 0% to 15%. The developed models showed a decrease in oil yield of 10% when 15% PS was interchanged with PET. Char content, acid number, and viscosity were shown to increase with the content of PET and lowered with the content of PS. PA caused an increase in char yield and viscosity, while it did not affect the acid number. The models R2-values varied from 0.87 to 0.96, showing that most of the variation in the responses can be explained by the differences in feed composition. The oil composition was found to mainly consist of hydrocarbons (C10 +), naphta and aromatics with only a small precense of alcohol and acid. The content of aromatic hydrocarbons is increased by the presence of PS, due to formation of styrene and toluene while the acid content increases with the PET content.

Effect of Sodium on the Evolution of Nitrogen Functionalities During Coal Pyrolysis : A Quantitative Experimental and Theoretical Investigation

ABSTRACT Understanding the migration and transformation of nitrogen during high-alkali coal pyrolysis and the influence of sodium on the nitrogen-containing components of coal is of great significance for the clean and efficient utilization of coal. In this study, gas chromatography-mass spectrometry (GC-MS), X-ray photoelectron spectroscopy (XPS) and ultraviolet visible spectroscopy (UV-Vis) were used to analyze the conversion of tar-N, char-N and gas-N during coal pyrolysis and the effect of sodium on the nitrogen-containing pyrolysis products of coal. The experimental results were combined with density functional theory (DFT) calculations to investigate the effect of sodium on the internal conversion process of char-N. The results revealed that a large amount of Na (2.5 wt.%, 3.5 wt.%) can reduce the nitrogen content in coal pyrolysis char, promote the formation of amine and amide in tar-N and inhibit the release of gaseous nitrogen. A small amount of Na (0.5 wt.%, 1.5 wt.%) retains nitrogen in char, reducing the total amount of nitrogen-containing species in the gas phase and tar, which is an effective means to inhibit the transformation of nitrogen to volatile matter. In addition, a large amount of Na promotes the conversion of pyrrole nitrogen (N-5) and pyridine nitrogen (N-6) in char to heterocyclic N in tar. A small amount of sodium promotes the hydrogenation and ring opening of heterocyclic-N in tar to HCN. Na promotes the conversion of N-5 and N-6 in char. DFT calculations further confirmed that the addition of Na significantly reduced the energy barrier of the rate determining step by about 36.6 kJ/mol.

Synergistic effect and chlorine migration behavior in co-pyrolysis of Pingshuo coal and polyvinyl chloride and directional chlorine enrichment using calcium oxide

Co-pyrolysis of waste plastics and low-rank coal is an important way to realize the recycling of plastic wastes and the clean and efficient conversion of coal. However, halogens released would cause equipment corrosion and affect tar quality when halogenated plastics were co-pyrolyzed with coal. For this reason, polyvinyl chloride (PVC), as a representative of halogenated plastic, was co-pyrolyzed with Pingshuo coal (PS) in a two-stage fixed-bed reactor. The synergistic effect between PS and PVC and the migration behavior of chlorine were investigated, and the in-situ removal of chlorine during pyrolysis was explored by adding a CaO bed in the second stage of the reactor. The results showed that the addition of PVC in PS has a positive synergistic effect on tar yield with a maximum tar yield increment of 2.30 wt% at 30 wt% PVC, which is related to the negative synergistic effect on gas yield. Furthermore, the addition of PVC increases the content of 1–3 ring aromatics and decreases the content of aliphatics in the tar. The chlorine content in char and tar increases significantly with the increase of PVC addition. The addition of a CaO bed can significantly reduce the yield of HCl and the chlorine content in the tar. At 700 ℃, the dehydrochlorination efficiency of CaO can reach 78.1%. However, the CO2 produced by PS pyrolysis will reduce the dehydrochlorination efficiency of CaO, and this effect of CO2 can be reduced by increasing the temperature of the CaO bed.

Catalytic and char-promoting effects of potassium on lignocellulosic biomass torrefaction and pyrolysis

Torrefaction is a potential pretreatment method to produce biochar used as a solid fuel or as an environmentally friendly construction material. However, the torrefaction performance varies when wood composition and mineral content change. Potassium (K) is an abundant mineral present in plants and is claimed to influence the degradation of lignocellulosic biomass. Therefore, a full understanding of the role of potassium is required to predict torrefaction behavior. Samples of beech, celluloses, hemicelluloses, and lignin were impregnated with different potassium carbonate K2CO3 concentrations (0.004, 0.008, and 0.012 M). Thermogravimetric analysis was utilized to analyze their thermal degradation characteristics under different temperatures. At 250 °C, the catalytic effect of potassium was weak. At 300 °C, potassium acted as a catalyst until a precise mass loss (65 wt%) and torrefaction duration (105 min) promoted char formation. The changed effect of this weight loss was possibly related to the relative increase in lignin content compared to cellulose and hemicelluloses While at a higher temperature (380 °C), the catalytic effect of potassium was rapid, and the increased char content was better observed. The potassium was found to act mainly on cellulose and hemicelluloses. After pyrolysis, the char weight increased with K up to 25.86 and 15.23 % for heating rates of 10 and 20 K min−1, respectively. FTIR and XRD showed that potassium did not significantly impact the structure or the crystallinity of wood at ambient conditions. The obtained results provide a novel insight into the role of potassium in the thermal treatment of biomass, with a better understanding of the thermal degradation mechanisms. This information could help to reduce the operating time and/or temperature, thus rendering torrefaction a green method for waste wood valorization.

Novel coal char-based cement grout: An experimental study on geotechnical and rheological properties

Coal char, a light and porous coal byproduct, is conventionally used for combustion and gasification, which leads to high carbon dioxide and other air pollutants emissions. In this study, the feasibility of using coal char in cement grout is evaluated. The coal char pyrolyzed at 850 °C is produced from Powder River Basin coal in Wyoming. Effects of char contents (up to 50%) and particle sizes (<300 μm and 300–850 μm) on geotechnical and rheological properties of char-cement grouts are comprehensively investigated. Compared to cement grout, the compressive strength of char-cement grout is 16% higher, and the final setting time is 55% shorter. The addition of coal char effectively reduces the bleeding in grouts without leading to a significant increase in Marsh viscosity. In general, coal char can provide many advantages towards improving engineering performance and broadening application of conventional cement grout.

Wet synthesis, characterization of goethite nanoparticles and its application in catalytic pyrolysis of palm kernel shell in TGA

Catalytic pyrolysis of biomass is a suitable means of obtaining high-yield bio-oil with reduced activation energy and char content. Goethite nanoparticles were synthesized via coprecipitation of FeCl2.4H2O and NaHCO3. TGA purged with N2 was used to study goethite’s catalytic effect on the thermal degradation of PKS. The obtained particles were characterized via instrumental analysis using BET, TEM, SEAD, and XRD gave multipoint SA of 309 m2/g & 0.276 cc/g; 18.33 nm; rings occurring at (101), (111), (021); and crystallinity of 51.51% with average size of 9.16 nm respectively. Their morphology was circular and needle-like shape. Its average crystallite size was 9.16 nm with a crystallinity of 51.51%. The 62.10% Fe in goethite was a suitable factor for its application as a catalyst in the thermal decomposition of PKS. The average Ea for uncatalyzed PKS were 53.45, 44.95, 47.09, 49.05 and 70.63 kJ/mol for order n =1, 0.30, 0.50, 0.67 and 2.00 respectively at the α of 0.2 while the average Ea for catalyzed PKS were 19.17, -17.70, 10.27, 12.64 and 52.69 kJ/mol for same order sequence at α of 0.71 using Coats–Redfern kinetics model. The goethite nanoparticles reduced Ea with higher α due to its special physicochemical properties.

Experimental investigation on sulfur transformation during coal steam gasification with Ca-based absorbent

To investigate the effects of temperature, Ca-based absorbent (CaO) and atmosphere on the sulfur transformation characteristics in coal steam gasification, experiments were conducted in a fixed-bed reactor. As temperature increased from 600 °C to 750 °C, H2S-S (sulfur in H2S) was elevated by 21.86% and absorbent-S decreased by 7.66%. More gaseous sulfur was captured by organic groups to form organic sulfur in char at higher temperature. CaO promoted the sulfur conversion, and played the role of gaseous sulfur absorbent at the same time, and showed an ability of organic sulfur removal. CaO slowed down the H2S release by reacting with it to form CaS, resulting in that the peak concentration of H2S without CaO reached 1026.7 ppm, which decreased to 426.3 ppm with CaO. The increase in Ca/C promoted the sulfur conversion slightly and reduced the sulfate content in char. Compared with inert atmosphere, H2S-S in the steam atmosphere increased by 35.07%, while absorbent-S decreased by 23.42%. The solid–solid reaction mechanism is more suitable for the sulfate transformation in inert atmosphere, while the gas–solid reaction mechanism is more suitable in steam atmosphere. The sulfur conversion in inert atmosphere was lower, but sulfate had a higher decomposition rate.

Efficient lead immobilization by bio-beads containing Pseudomonas rhodesiae and bone char

Mineralization of lead ions (Pb2+) to pyromorphite using phosphorus-containing materials is an effective way to remediate lead (Pb) contamination. Bone char is rich in phosphorus, but its immobilization of Pb2+ is limited by poor phosphate release. To utilize the phosphorus in bone char and provide a suitable growth environment for phosphate-solubilizing bacteria, bone char and Pseudomonas rhodesiae HP-7 were encapsulated into bio-beads, and the immobilization performance and mechanism of Pb in solution and soil by bio-beads were investigated. The results showed that 137 mg/g of phosphorus was released from bone char in the presence of the HP-7 strain. Pb2+ removal efficiency reached 100 % with an initial Pb2+ concentration of 1 mM, bone char content of 6 g/L, and bio-bead dosage of 1 %. Most Pb2+ was immobilized on the surface of the bio-beads as Pb5(PO4)3Cl. The soil remediation experiments showed a 34 % reduction in the acid-soluble fraction of Pb. The bio-beads showed good stability in long-term (30 d) soil remediation. The present study shows that bone char can be turned into an efficient Pb immobilization material in the presence of phosphate-solubilizing bacteria. Thus, bio-beads are expected to be used in the remediation of Pb-contaminated environments.