Metal Removal Efficiency Research Articles

Potential of biochar and humic substances for phytoremediation of trace metals in oil sands process affected water

Oil sands process affected water (OSPW) is produced during bitumen extraction and typically contains high concentrations of trace metals. Constructed wetlands have emerged as a cost effective and green technology for the treatment of metals in wastewaters. Whether the addition of amendments to constructed wetlands can improve metal removal efficiency is unknown. We investigated the synergistic effects of carbon based amendments and wetland plant species in removal of arsenic, cadmium, cobalt, chromium, copper, nickel, and selenium from OSPW. Three native wetland species (Carex aquatilis, Juncus balticus, Scirpus validus) and two amendments (canola straw biochar, nano humus) were investigated in constructed wetland mesocosms over 60 days. Amendment effect on metal removal efficiency was not significant, while plant species effect was. Phytoremediation resulted in removal efficiencies of 78.61–96.31 % for arsenic, cadmium, and cobalt. Carex aquatilis had the highest removal efficiencies for all metals. Amendments alone performed well in removing some metals and were comparable to phytoremediation for cadmium, cobalt, copper, and nickel. Metals were primarily distributed in roots with negligible translocation to shoots. Our work provides insights into the role of plants and amendments during metal remediation and their complex interactions in constructed treatment wetlands.

Insights into PVC-promoted hydrothermal carbonization of manure: Dechlorination, inorganic metals removal, and combustion behaviors

Hydrothermal carbonization (HTC) can serve as a promising route to effectively co-valorize biomass and plastic wastes for solid fuel production. However, manure-derived hydrochar for fuel application remains a significant challenge due to its high ash content and low energy density. Polyvinyl chloride (PVC), as a chlorine-containing plastic, subjected to HTC commonly results in the generation of massive acidic wastewater. Herein, we proposed a PVC-promoted HTC route for high energy–density hydrochar production. By utilizing PVC as an in situ acidic additive, the HTC condition was optimized at 275 °C, 30 min, with a PVC addition of 10 %. The hydrochar obtained under the optimized condition exhibited a higher heating value (HHV) of 25.89 MJ/kg, comparable to bituminous coals, and achieve a high energy recovery rate of nearly 70 %. Moreover, the excellent removal efficiencies of inorganic metals and chlorine both exceeding 95 % (except for Fe at 86 %) were observed, owing to the strong interactions between dechlorination and inorganic metals removal. Importantly, it was evidenced that acidic reaction environment was demonstrated to enhance the carbonization degree and modify the hydrochar formation mechanism. Furthermore, the high comprehensive combustion index S of 3.22 × 10−7 %2/( °C3·min2) and low average Ea of 134.20 kJ/mol were achieved, indicating the favorable combustion behaviors. Overall, this work systematically and comprehensively investigated the PVC-promoted HTC of manure waste for advanced solid fuel production and examined its combustion characteristics, unveiling the hydrochar formation mechanism.

Coupling of bioleaching and electrokinetic soil flushing for the in-situ removal of impurity from Pb-Zn mine tailings

This study combines bioleaching and electrokinetics (EK) for the in-situ removal of metals from polluted mine tailings collected from an abandoned Pb-Zn mine. The proposed treatment strategy consisted in the external production of an acid bioleaching (BL) medium in a bioreactor by means of autochthonous acidophilic microorganisms incubated from real mine tailings; next, the BL medium was subsequently used as anolyte and placed in contact in situ with the polluted soil, taking advantage of EK mechanisms r for dissolution and transport of metals to the cathode compartment. After obtaining a microbial culture capable of producing the bioleaching medium, lab-scale EK experiments were performed, and the influence of the voltage dosage (0.5, 1.0 and 1.5 V cm−1) was assessed. The results obtained showed that the BL medium improved the metal removal efficiency, and that the applied voltage gradient had a clear influence. Specifically, the combination of an electric current under 1.5 V cm−1 and the BL medium increased the metal removal rates by 17 % (Fe), 4 % (Cu), 2 % (Zn), 12 % (Mn), 12 % (Ni), 1 % (Cr) and 7 % (Co), as compared to those without using BL. With this novel treatment, it was also possible to comply with the local regulatory requirements for most of the metals studied. This technology offers several advantages over other EK-bioleaching configurations previously reported. It was found that the limiting factor in the process was the voltage gradient applied, as higher voltages increased metal removal yields but also producing higher soil heating with the consequent energy losses.

An overview of heavy metals treatment & management for laboratory waste liquid (LWL)

The laboratory waste liquid (LWL) is the discarded liquid after the completion of analysis and is produced from the testing laboratories including regulatory institutions, colleges, universities and research organizations. This LWL is laden with a variety of heavy metals due to the use of heavy metal salts in analysis and the treatment and safe disposal of LWL is seldom given due consideration. Thus, the management of hazardous laboratory waste liquid (HLWL) containing heavy metals is essential at the source itself. Accordingly, this article presents systematic review of three processes for heavy metals removal viz. precipitation, adsorption, and membrane separation. The review covers various factors such as heavy metal removal efficiencies & concentration ranges, optimum pH, most frequently studied methods, less studied aspects, its commercial availability, operational ease, and the potential of risk minimization with due concern to toxic heavy metals. The concentrations of heavy metals in LWL is also presented. Based on the review, activated carbon (AC) adsorption appears to be the best option for LWL having heavy metals concentration of less than 10 mg/L. The heavy metals removal efficiency of more than 95% can be achieved at an AC dose of 0.2–1 g/L. The hydroxide precipitation was found to achieve more than 95% removal efficiencies at higher heavy metals concentrations. Thus, for concentrations higher than 10 mg/L up to 3000 mg/L, the hydroxide precipitation followed by activated carbon adsorption may prove beneficial.

An Ionic Liquid-Based Biorefinery Approach for Duckweed Utilization.

This study establishes a foundation for the ionic liquid (IL) pretreatment of duckweed biomass. An optimized IL-based process was designed to exploit the unique properties of duckweed including efficient metal removal, potential starch accumulation, and protein accumulation. Two ILs, namely, dimethylethanolammonium formate ([DMEtA][HCOO]) and N,N-dimethylbutylammonium hydrogen sulfate ([DMBA][HSO4]), were investigated for the pretreatment of two duckweed species (Spirodela polyrhiza and Lemna minor). The evaluation focused on starch recovery, sugar release, protein recovery, and metal extraction capabilities. [DMEtA][HCOO] demonstrated near-quantitative starch recoveries at 120 °C, while [DMBA][HSO4] showed similar performance at 90 °C within a reaction time of 2 h. Saccharification yields for most pulps exceeded 90% after 8 h of hydrolysis, outperforming "traditional" lignocellulosic biomasses such as miscanthus or sugarcane bagasse. Approximately 50 and 80 wt % of the protein were solubilized in [DMEtA][HCOO] and [DMBA][HSO4], respectively, while the remaining protein distributed between the pulp and lignin. However, the solubilized protein in the IL could not be recovered due to its low molecular weight. Regarding metal extraction, [DMEtA][HCOO] demonstrated higher efficiency, achieving 81% removal of Ni from Lemna minor's pulps, whereas [DMBA][HSO4] extracted only 28% of Ni with slightly higher pulp concentrations. These findings indicate the need for further optimization in concurrent metal extraction using ILs.

Spatial and temporal variations in environmental impacts of heavy metal emissions from China's non-ferrous industry: An enterprise-specific assessment

In China, the non-ferrous metal industry is the sector with the highest emissions of arsenic, cadmium, mercury and lead, causing serious impacts on human health and the ecosystem. However, current heavy metal emission inventories are inadequate for figuring out their exposures and associated environmental impacts due to the lack of detailed data. Here, we constructed a high-resolution, enterprise-specific, and long-term dataset detailing heavy metal emissions from the non-ferrous industry in China from 1981 to 2020, using comprehensive enterprise information. Furthermore, an environmental impact assessment was performed using the characterization factors of the IMPACT World + model. Results show that: (1) from 1981 to 2020, the total heavy metal emissions of China's non-ferrous industry reached 144,697 tons (t), with atmospheric emissions (104,524 t) exceeding aquatic ones (40,173 t). (2) The industry's emissions showed a rising and then declining trend, with significant spatial heterogeneity, where heavy metal emissions concentrated in the central and western parts of Yunnan, the southern part of Hunan, the northern part of Guangxi, Henan along the Yellow River, the intersection of Gansu and Shaanxi, the central and eastern parts of Liaoning, and the eastern part of Inner Mongolia. (3) The environmental impact on human health was 1.19 × 107 DALY, and the value of ecosystem quality was 7.26 × 109 species·yr. The top 10 % of enterprises with the largest environmental impacts contributed over 60 % of human health risks and 62 % of ecosystem quality impacts. Improving the removal efficiency of heavy metals by 10 % within the four major industry classes could lead to a 9.92 % reduction in human health impacts and a 9.77 % reduction in ecosystem quality impacts within the non-ferrous metals industry. The findings of this study can provide insights for pollution control, environmental risk reduction, and sustainable development in the non-ferrous metals industry.

Optimum conditions for growth and copper (II) removal from leachate by Chlorella vulgaris, Spirogyra ellipsospora and Ulva lactuca

This study examined the effectiveness of removing copper (Cu (II)) ions from leachate using three different live algae species (Chlorella vulgaris, Spirogyra ellipsospora, and Ulva lactuca), both individually and in combination. Various algal doses were tested to assess their impact on metal removal efficiency and algal growth. Five distinct masses (5, 10, 15, 20, and 25 g L−1) of each alga were grown in a batch experiment on leachate containing 3 mg L−1 of Cu (II) ions. It was found that the optimum algal dose is between 12.5 and 17.5 g L−1, and the optimum equilibrium duration was between 3 and 4.5 days for tested algal species. Under the optimum conditions of algal dose and contact time, the algae exhibited growth and Cu (II) ions removal efficiency in the order of Spirogyra ellipsospora > mixed algae > Chlorella vulgaris > Ulva lactuca. The study concludes that the selection of right algal species is crucial to optimize the growing environment for copper-contaminated leachate bioremediation.

High-efficiency combination washing agents with eco-friendliness simultaneously removing Cd, Cu and Ni from soil of e-waste recycling site: A lab-scale experiment

Soil washing technology plays an important role in the removal of heavy metals, and the efficacy of this process depends on the washing agent used. Due to the difficulty in treating soils contaminated by multiple heavy metals, there is still a need for further exploration of efficient washing agents with low environmental impact. Although single washing agents, such as chelators, can also effectively remove heavy metals from soil, combining efficient washing agents and determining their optimal washing conditions can effectively improve their removal efficiency for multiple heavy metals in soil simultaneously. Based on the previous research, the present study was carried out to combine different types of washing agents to remediate contaminated soils at a commonly e-waste recycling site. The objectives were to investigate their efficient washing conditions and assess the impact of the washing process on the speciation distribution and pollution level associated with heavy metals in soil. The results showed that the combination of HEDP (1-hydroxyethylidene-1,1-diphosphonic acid) and FeCl3 at a ratio of 6:4 exhibited the most effective removal of Cd, Cu and Ni from the contaminated soil at an e-waste recycling site. Under optimal washing conditions, with a soil-to-liquid ratio of 1:20 and a washing time of 48 h, the removal rates of Cd, Cu and Ni were 96.72%, 69.91% and 76.08%, respectively. It needed to be emphasized that the combination washing agents were able to remove most of the acid-soluble, reducible and oxidizable fractions of heavy metals, and even the removal rates of the stable residual fraction (e.g., of Cd) was at a relatively high level. In addition, the washing process significantly reduced the pollution level associated with heavy metals in soil. This study aid in the development of combined efficient washing agents and explores optimal washing strategies for the remediation of Cd, Cu, and Ni-contaminated soil at e-waste recycling sites. The findings may play a role in enhancing the remediation capabilities for soils contaminated with multiple heavy metals, due to its characteristics of and high-efficiency and environmental friendliness.

Enhanced heavy metal leaching from volcanic muds: Synergistic effects of citric acid and EDTA composite system

The soil leaching technology is a well-established technique commonly employed for the remediation of soils contaminated with heavy metals. Volcanic muds share similar properties to those of soil. This study utilizes soil leaching technology to tackle the presence of heavy metals in volcanic muds. It examines the leaching removal effect of the synergistic system of organic acid citric acid (CA) and chelating agent EDTA on heavy metals Pb, Cd, Cr, and Ni in volcanic muds. The leaching conditions were initially selected and subsequently optimized through the application of response surface methodology (RSM). The priority of leaching conditions can be ranked as follows: leaching duration is found to be more crucial than leaching agent concentration, which is noted to be more pivotal than the solid-liquid ratio. Following an in-depth evaluation of model predictions and experimental validation, it has been established that the optimal leaching concentration of EDTA is 0.15 mol·L−1, the optimal leaching duration is 9 h, and the optimal solid-liquid ratio is 1:10. For the compound CA, the most effective leaching concentration is 0.3 mol·L−1, the optimal leaching duration is 8 h, and the optimal ratio of solid to liquid is 1:10. The significance of the leaching conditions was further explored in conjunction with RSM. Furthermore, the integration of both leaching methods, namely combined leaching and stepwise leaching, has been demonstrated to amplify the removal efficiency of heavy metals, with stepwise leaching showing the highest removal rate. The experimental findings suggest that the leaching technique involving CA and EDTA composite system is an effective approach for the remediation of heavy metals such as Pb, Cd, Cr, and Ni in volcanic muds. This study provides theoretical rationale for the adoption of soil leaching technology in the remediation of heavy metals in volcanic muds. Additionally, the heavy metal content of the remediated volcanic muds substantially meets with the standards for cosmetic raw materials.

Sustainable solutions for desalination plant outfall brine: Modified halloysite nanoclay-based remediation of heavy metals and salinity

The aim of this research is to craft a material that effectively curbs the higher level of heavy metals and salinity in brine from desalination plants. Through thorough experimentation, an optimized form of Halloysite Nanoclay was achieved, which was further enhanced with 8-hydroxyquinoline for increased metal removal efficiency. The enhanced nanoclay's adsorption capabilities were carefully fine-tuned, displaying a type III adsorption isotherm and a significant surface area (72.8 m² g–1). The modified Halloysite nanoclay demonstrates improved efficiency in removing metal ions, achieving rates of 79.12 % for Zn, 83.33 % for Fe, 81.18 % for Ni, and 79.81 % for Cu. Notably, this advanced material proved its prowess in purifying heavy metals. The prepared material displayed noteworthy recycling capacity, substantiated through a series of experiments. This study highlights the effectiveness of using modified Halloysite nanoclay to treat desalination plant brine sustainably, opening avenues for further research and practical applications in this area.

Heavy metals removal from synthetic and industrial wastewater using synthesized zinc oxide nanoparticles

With the advancement in wastewater treatment systems over conventional systems the application of nanotechnology has gained popularity in the past decade. The process can be applied by modifying the physico-chemical properties of metal oxides that increase their effectiveness in extracting heavy metals from wastewater. The present study has been carried out by synthesizing the Zinc oxide nanoparticles using green and chemical synthetic methods. Green-synthesized ZnO nanoparticles (GS-ZnO-NP) were discovered to exhibit a maximum removal effectiveness of 93% and 94% for heavy metals in industrial wastewater and synthetic wastewater, respectively. However, heavy metals removal efficiency from industrial and synthetic wastewater was observed to be 98% and 98% respectively using chemically synthesized ZnO nanoparticles (CS-ZnO-NP). The heavy metals removal efficiency for specific metal is observed to be Cr > Pb > Cu > Hg > As. The kinetics of adsorption was calculated using Freundlich and Langmuir isotherm models. Freundlich model is the best fit with the coefficient of correlation in the range of 0.71–1 for green synthesized and 0.82 to 0.95 for chemically synthesized ZnO nanoparticles.

Mechanisms of copper and zinc bioremoval by microalgae and bacteria grown in nutrient rich wastewaters

Swine farming produces large quantities of nutrient-rich wastewater, which often contains metals such as Cu and Zn, used as feed additives for pigs. These metals must be removed from the wastewater before discharge but their retention in the biomass can limit its subsequent utilization. Photobioreactors are a very promising alternative for swine wastewater treatment, as the consortium of microalgae and bacteria growing symbiotically in these reactors allows high nutrient and metal removal efficiency at moderate costs. This work studies the mechanisms of removal of Cu(II) and Zn(II) by the two types of microorganisms growing in these photobioreactors. A microalga commonly used in wastewater treatment (Scenedesmus almeriensis) and an activated sludge were kept in contact with synthetic wastewater containing 100 mg/L of Cu and Zn. After 72 h, Scenedesmus almeriensis removed 43% of Cu and 45% of Zn, while activated sludge removed 78% of Cu and 96% of Zn. Single and sequential extractions of the biomasses using different extracting reagents revealed that biosorption on protonable groups is the dominant removal mechanisms. Mild reagents solubilized 69% of Cu and 94% of Zn from the microalgae and 76% of Cu and 93% of Zn from the activated sludge. Low metal concentrations in the oxidizable and residual fractions evidenced minimal bioaccumulation inside the cells. FTIR and ESEM-EDX analysis confirmed biosorption by ion exchange and complexation as the main metal remediation mechanisms. The weak bonds of the biosorbed Cu and Zn ions are beneficial for the valorization of biomass and the obtaining of safe bioproducts.

A comparative study on heavy metal (cadmium) tolerance and biosorption capacity of locally isolated lactic acid bacteria

Heavy metals (HM) have less biological role but show extreme toxicity in living systems. Lactic acid bacteria (LAB) are beneficial microorganisms, some of which have the ability to chelate HM and may be used to treat heavy metals poisoning. The aim of the current study was to select and identify Cd-removing probiotic LAB strains, for future pharmaceutical application. Seventeen LAB strains, from human excretions and animal fecal matter, were initially verified for their probiotic properties. The strains which could survive in the presence of Cd (≥100 ppm) were selected. The metal removal efficiency of isolates was compared, through atomic absorption spectrophotometry (AAS), by measuring the reduction in Cd contents of CdCl2 5 mg/L (3.05 ppm of Cd) supplemented broth following 24 h culturing of the strains. The Cd reduction of 38–75% was recorded in culture broth. The Cd removal ability significantly varied (p < 0.05) with microbial surface charge, incubation period, temperature and pH of media. Levilactobacillus brevis MW362790 and Pediococcus pentosaceus MT323062, identified through 16S rRNA gene sequencing, were recognized as strong Cd chelators. These strains may have application in pharmaceutical or agriculture (farm animals) for protection against cadmium toxicity. Further studies are suggested on in vivo metal detoxification potential.

Isolation, characterization, identification, genomics and analyses of bioaccumulation and biosorption potential of two arsenic-resistant bacteria obtained from natural environments

Arsenic (As) is a significant contaminant whose unrestrained entrance into different ecosystems has created global concern. At the cellular level, As forms unsteady intermediates with genetic materials and perturbs different metabolic processes and proper folding of proteins. This study was the first in this region to explore, isolate, screen systematically, and intensively characterize potent As-tolerant bacterial strains from natural environments near Raiganj town of Uttar Dinajpur, West Bengal. In this study, two potent Gram-negative bacterial strains with high tolerance to the poisonous form of As, i.e., As(III) and As(V), were obtained. Both the isolates were identified using biochemical tests and 16S rRNA gene sequencing. These bacteria oxidized toxic As(III) into less poisonous As(V) and depicted tolerance towards other heavy metals. Comparative metabolic profiling of the isolates in control and As-exposed conditions through Fourier-transform infrared spectroscopy showed metabolic adjustments to cope with As toxicity. The metal removal efficiency of the isolates at different pH showed that one of the isolates, KG1D, could remove As efficiently irrespective of changes in the media pH. In contrast, the efficiency of metal removal by PF14 was largely pH-dependent. The cell mass of both the isolates was also found to favourably adsorb As(III). Whole genome sequence analysis of the isolates depicted the presence of the arsRBC genes of the arsenic operon conferring resistance to As. Owing to their As(III) oxidizing potential, high As bioaccumulation, and tolerance to other heavy metals, these bacteria could be used to bioremediate and reclaim As-contaminated sites.

The application of machine learning methods for prediction of heavy metal by activated carbons, biochars, and carbon nanotubes

Carbonaceous materials are commonly used as adsorbents for heavy metals. The determination of the adsorption capacity needs time and energy, and the key factors affecting the adsorption capacity have not been determined. Therefore, a new and efficient method is needed to predict the adsorption capacity and explore the decisive factors in the adsorption process. In this study, three tree-based machine learning models (i.e., random forest, gradient boosting decision tree, and extreme gradient boosting) were developed to predict the adsorption capacity of eight heavy metals (i.e., As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn) on activated carbons, biochars, and carbon nanotubes using 3674 data points extracted from 151 journal articles. After a comprehensive comparison, the gradient boosting decision tree had the best performance for a combined model based on all data (R2 = 0.9707, RMSE = 0.1420). Moreover, independent models were developed for three datasets classified by the adsorbent and eight datasets classified by the heavy metals. In addition, a graphical user interface was built to predict the adsorption capacity of heavy metals. This study provides a novel strategy and convenient tool for the removal of heavy metals and can help to improve the removal efficiency of heavy metals to build a healthier world.

Lysine-functionalized graphene oxide on cost-effective microporous support: A hydrophilic and fouling resistant membrane for safe lead filtration

The presence of heavy metals in freshwater is a severe problem humanity faces. Remedies with high removal efficiency of heavy metals from contaminated water are crucial. However, existing studies often neglect effluent quality per World Health Organization (WHO) standards. Also, the reported conditions are either unrealistic to the actual contamination levels or unsuitable for large-scale applications. Here, we report the fabrication of zwitterionic graphene oxide (GO) by incorporating a pH-responsive group (i.e., Lysine) using N, N′-diisopropylcarbodiimide (DIC) as a coupling agent. The modified GO-Lys was then coated on a commercially available 0.45-μm Nylon membrane and was tested for selective removal of toxic heavy metals from synthetic water and human blood plasma samples while allowing essential metal ions. Consequently, lead was the most retained toxic metal (i.e., 99.99% retention with effluent quality meeting WHO standards) among nickel, arsenic, cadmium, and mercury (i.e., between 50 to 80% retention). These composite membranes also displayed excellent fouling resistance and inhibited bacterial adhesion onto the membrane surface, while maintaining stable performance over a long time and critical transmembrane pressure conditions. This research marks a significant advancement in environmental technologies, providing an effective solution for selectively removing heavy metal pollutants, with a particular focus on lead detoxification applications.

Application of coconut shell activated carbon filter in vertical subsurface flow constructed wetland for enhanced multi-metal bioremediation and antioxidant response of Salvinia cucullate

Coconut shell activated carbon (CNSAC) was applied as a filter layer in hybrid vertical subsurface flow constructed wetland (H-VSSF-CW), in order to enhance the multi-metal removal efficiency of the constructed wetland (CW) and to reduce heavy metal accumulation on Salvinia cucullata. Treatment P + AC, (having CNSAC filter layer), showed 32, 21 and 34% more Cd, Cr, and Pb removal efficiency than treatment P (without CNSAC layer). CNSAC activated carbon adsorbed Cd and Pb and Cr by functional groups –NH, -NO2, -C-O, –OH and –CO, and significantly reduced Cd and Pb exposure to S. cucullate. Chromium adsorption by CNSAC filter layer was half (just 25% of total input) of the Cd and Pb. In treatment P, due to high Cd, Pb and Cr accumulation in S. cucullate, the antioxidant defense mechanism of the plant was collapsed and cell death was observed, which in turn has resulted reduced biomass gain (5% reduction). On the other hand, in treatment P + AC, an antioxidant defense mechanism was active in the form significantly (p ≤ 0.05) increased of SOD, CAT and proline content while reduced MDA, EL, %EB and soluble sugar. So, the application of CNSAC increased the heavy metal removal efficiency of H-VSSF-CW by adsorption of a considerable share of heavy metal and hence, reduced the heavy metal load/exposure to S. cucullate.

Mn&lt;sup&gt;2+&lt;/sup&gt; Adsorption on Nanozeolite: Determination of Thermodynamic Properties Using Isothermal Titration Calorimetry

This study investigates the thermodynamics of manganese ion adsorption on nanozeolite to assess the nanomaterial’s heavy metal removal efficiency from surface water, industrial water, and groundwater. Using Isothermal Titration Calorimetry (ITC), the thermodynamic profile of nanozeolite is obtained, demonstrating a low equilibrium binding affinity. The thermodynamic signature showed favorable binding mechanisms, primarily from the change of entropy, suggesting spontaneous reactions. Meanwhile, the enthalpy change of adsorption increases as temperature rises, while ∆G and T∆S decrease. Using proper thermodynamic conditions, nanozeolite may efficiently remove manganese from different water sources.

Hydrothermal carbonization of corncob for hydrochar production and its combustion reactivity in a blast furnace.

A key factor restricting the application of biochar in the steel industry is its high-quality upgrading. This paper evaluated the characteristics of hydrochar produced by HTC (hydrothermal carbonization) process of corncob to be used as a solid fuel. HTC temperatures (240-300°C) and HTC water-reused times (1-3 times) were examined for their effects on hydrochar yield, physicochemical characteristics, and combustion properties. The results showed hydrochar yields, O/C, and H/C parameters decreased as HTC temperature and water-reused times increased, while its high heating value increased. Due to dehydration and decarboxylation, hydrochar showed similar characteristics to those in bituminous coal. The removal efficiency of alkali metal K reached 99% after HTC treatment. Carbonaceous hydrochar had become more compact, orderly, and stable with increasing amounts of aromatic functional groups, C = C, and C = O. Hydrochar, as a biofuel, has higher ignition energy and is more stable than corncob due to its high carbonaceous order degree. To calculate combustion kinetic parameters, the Kissinger-Akahira-Sunose (KAS) and Flynn-Wall-Ozawa (FWO) methods were applied. The results revealed that Eα (average activation energy) was quite similar between the two models. HC-300 had an Eα of 262kJ/mol. HTC could be an efficient way to reutilize corncob biomass into clean biofuels with high calorific value.

Enhanced Heavy Metal Removal from Wastewater Produced by Chemical Analysis Laboratory Using Calcium Oxide Precipitation: pH Improvement and Characterization of Precipitated Phases

This article presents research results on the precipitation of heavy metals: Aluminum (Al), arsenic (As), cadmium (Cd), zinc (Zn), iron (Fe), chromium (Cr), copper (Cu), nickel (Ni), vanadium (V), and molybdenum (Mo) from wastewater generated in mining chemical analysis laboratory. Calcium oxide was used as the precipitating agent. The efficiency of heavy metal removal was achieved by increasing the dosage of precipitating reagent (8-28 g/L). Efficiencies greater than 90% are achieved. The efficiency of chemical precipitation depends on the pH of the process. Over a wide pH range from 6-11, the removal efficiency of zinc, iron, cadmium, and arsenic were approximately 99.9%. The optimum pH range for the removal of most elements was found to be between 8 and 11, where the removal efficiency of heavy metal ions reached up to 99%. Furthermore, X-ray diffraction results indicated that the metals in the wastewater precipitated in various forms as mentioned in Table 7, and not just as hydroxides, due to the presence of different ions in the solution.