Adsorption of Cd(II) from aqueous solutions by rape straw biochar derived from different modification processes

In this study, adsorption experiments on Cd(II) ions in aqueous solution by biochars pyrolyzed from millet bran (MBBC) at 400~800 °C were carried out and MBBC had superior adsorption performance at pyrolysis temperature of 600~800 °C. Then, biochars were modified by potassium permanganate (MBBC-PP), potassium ferrate (MBBC-PF), and citric acid (MBBC-CA). The results showed that the adsorption capacities of these adsorbents were in the order: MBBC-PP > MBBC-PF > MBBC-CA > MBBC. FT-IR, XRD, and Raman were used to determine the characteristics of biochars and explore the main adsorption mechanism causing by modification. These characterizations confirmed that manganese oxide and iron oxide particles were loaded on the surface of MBBC-PP and MBBC-PF, respectively. For MBBC-PP and MBBC-PF, the adsorption sites generated by the loaded metal oxides play more important role than other factors in Cd(II) adsorption. For MBBC-CA, surface functional groups were the main contributor during Cd(II) adsorption. Batch adsorption experiments demonstrate a Langmuir model fit for Cd(II). The sorption kinetics of Cd(II) on adsorbents follows pseudo-second-order kinetics. Modified biochars, especially the one modified by KMnO4, could act as effective alternatives to enhance heavy metals removal from aqueous solutions.

Mechanisms for cadmium adsorption by magnetic biochar composites in an aqueous solution.

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.

Adsorption of cadmium (II) ions from aqueous solution by a new low-cost adsorbent—Bamboo charcoal

This study was conducted in order to understand the mechanism of Cd and Pb adsorption in aqueous solutions by raw and modified saw dust (SD) of Alstonia macrophylla. The biosorbent was characterized by Boehm titration, specific surface area, scanning electron microscopy (SEM), X-ray energy dispersion (EDAX), and Fourier transform infrared (FTIR) analyses. SD was treated using organic acids and bases. Batch studies were conducted for raw and modified SD to determine the effect of initial concentration, pH, ionic strength, and contact time on metal adsorption. The specific surface area and total basic and acidic groups of SD were 77 m2/g and 1521 and 2312 μmol/g, respectively. The adsorption of both metals onto SD was pH dependent. No ionic strength dependency was observed in adsorption of Cd and Pb at pH >6, indicating inner sphere surface complexation. Monolayer adsorption is dominant in both metal sorptions by SD. Furthermore, there is no competition between metals on adsorption and raw SD was found to be suitable for removal of Cd and Pb as compared to organic acid– or base-treated SD. Maximum adsorption capacity of SD for Cd and Pb were 30.6 and 204.2 mg/g, respectively. Results indicate that the A. macrophylla SD can be considered as a potential material for metal ion removal from wastewater.

Removal of cadmium and lead from aqueous solutions by thermal activated electrolytic manganese residues

Use of conventional or non-conventional treatments of biochar for lipase immobilization

This study evaluated the cadmium (Cd) adsorption characteristics of sugarcane bagasse (BG) calcined at different temperatures (200-1000°C). The point of zero charge (pHpzc) of the BGs ranged from 4.3 to 6.5. The amount of Cd adsorbed was higher at pH 4-8 than at pH 2. These results indicate that the negative charge on the BG surface and the presence of Cd(II) cations are important for Cd adsorption. Meanwhile, the amount of Cd adsorbed and the specific surface area (SSA) of BG increased with increasing calcination temperature of BG. Furthermore, a partial correlation analysis revealed that acidic surface functional groups (SFGs) were also significantly associated with Cd adsorption, independently of SSA. These results suggest that both SSA and acidic SFGs jointly contribute to Cd adsorption.

Diatomite is an economical and environmentally friendly adsorbent, and its use has been applied widely for the treatment of water contaminated by heavy metals. Despite this, the mechanism for the removal of the heavy metal Cd(II) remains unclear. In this work, we explored the adsorption mechanism of Cd(II) by diatomite using batch experiment, and characterized the diatomite using scanning electron microscopy, energy-dispersive spectrometry, specific surface area, and pore size distribution analysis. Our results showed that, under the experimental conditions, the kinetic adsorption approached equilibrium within 5min, and the Sips isotherm model was most suitable for data fitting. EDS characterization of the Cd-loaded diatomite indicated that Cd(II) was adsorbed onto the diatomite. Furthermore, desorption experiments showed that Ca2+ and Mg2+ in the diatomite caused an ion exchange interaction, and this was primarily responsible for Cd(II) adsorption. Moreover, we found that its contribution to the whole adsorption reaction could reach 80%, while the remainder of Cd(II) was probably trapped in the microporous structure of the diatomite. Additionally, our data indicated that the adsorption mechanism did not change significantly after regeneration. These results have provided special insight into the deep understanding of the mechanism of Cd(II) adsorption by diatomite, and could provide theoretical support and guidance for further development and application of diatomite in the treatment of Cd(II)-contaminated water. Graphical abstract.

Enhancing Cd(II) adsorption on rice straw biochar by modification of iron and manganese oxides

Novel Fe-Mn binary oxide-biochar as an adsorbent for removing Cd(II) from aqueous solutions

Formation and properties of nanostructured colloidal manganese oxide particles obtained through the thermally controlled transformation of manganese carbonate precursor phase

In this study, hydrochar and pyrochar were made from cellulose, lignin (components of biomass), and corn husk (a type of biomass) through hydrothermal carbonization at 300 ℃ and pyrolysis at 300 ℃ and 500 ℃. Their physiochemical properties and Cd(Ⅱ) adsorption performances were then compared. Additionally, characteristics of hydrochar and pyrochar generated by each process were analyzed, including char generation yield, proximate & ultimate analysis, specific surface area (BET surface area) & porosity analysis, SEM & EDS (Scanning Electron Microscope & Energy Dispersive Spectrometer), FT-IR, pHpzc, and so on. The pyrochar generated at the same temperature (300 ℃) had higher char generation yield, ash content, and oxygen content with more oxygen functional groups than hydrochar. However, pyrochar had a lower specific surface area and pore volume than hypercar. By type of biomass, lignin showed the highest char generation yield. Regarding pHpzc, corn husk had the highest value, followed by lignin and cellulose. Cd(Ⅱ) adsorption characteristics in hydrochar and pyrochar were more suitable for the Langmuir adsorption model. It was found that the Cd(Ⅱ) adsorption amount (116.8 mg/g) was the highest in PC-CH-500, which had high pHpzc and inorganic content. As a result, electrostatic adsorption and cation exchange were the main mechanisms of Cd(Ⅱ) adsorption under the condition of pH solution < pHpzc.

In this work, a batch adsorption study was conducted to investigate the removal efficiency of lead (II), Copper (II) and Cadmium (II) from aqueous solutions by (poly (thiourea-Formaldehyde-Epoxy resin) nanomagnetic Full-IPN's (NM Full-IPN's). The NM Full-IPN's was synthesized by sequential polymerization with presence Fe3O4 nanoparticles. The chemical structure and surface morphology of NM Full-IPNS resin nanoparticles were characterized by Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM). The chemical structure and surface morphology of NM Full-IPNS resin nanoparticles were characterized by Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM). The thermal properties of (NM Full- IPN's) has been evaluated by Thermogravimetric analysis (TGA) and Differential Scanning Calorimetric (DSC). Adsorption of Pb (II), Cu(lI) and Cd(II) onto NM Full- IPN's agreed well with the Langmuir model, as revealed by the higher values of correlation coefficients. The results indicate that NM Full- IPN's could be used as efficient adsorbent for the removal of Pb (II), Cu(lI) and Cd(II) from aqueous solution

Purpose – In this research, we have prepared activated carbon (AC) from the waste of banana peels (Musa acuminate L.) using potassium hydroxide (KOH) for carbon monoxide (CO) adsorption from motorcycle gas emission. Design/Methodology/Approach – The activation was conducted using a chemical activator (KOH) at various concentrations of 1, 2, and 3 N for 1, 2, and 3 h, respectively. Characteristics of banana peels AC (BPAC) produced were analyzed using the Fourier-transform infra-red spectroscopy and scanning electron microscopy. Findings – Results showed that KOH concentration and activation time strongly affected the CO adsorption and opening of the AC surface pore. There was an increase in the CO sorption when the KOH concentration was increased up to 3 N concentration. The highest CO adsorption from the emission occurred at 70.95% under KOH concentration of 3 N during the 3-h preparation. Research Limitations/Implications – BPAC has been used as an adsorbent for only CO from motorcycle gas emission but not as an adsorbent for HC, NO, NOx, or H2S. Practical Implications – BPAC can be used as the potential adsorbent for the removal of CO from motorcycle gas emission, and it is an environmental friendly, low cost, and easy to make adsorbent. Originality/Value – In this study, the AC is made from biomass and is used in wastewater treatment, but limited studies are found on the removal of CO from motorcycle gas emission.