Removal of nitrite ions from water by adsorption on chemically activated carbon

Despite the many articles about activated carbon with different precursors in adsorption process, no in-depth research has been carried out to understand the causes of the difference in surface adsorption characteristics of activated carbon with different precursors and different activation processes. In this work, the ability of two active carbon adsorbents made of walnut shell and peach kernel by two chemical and physical methods (totally 4 different types of activated carbon) in treatment of oily wastewater including diesel, gasoline, used oil or engine lubricant has been compared. The results show that the chemical activated peach carbon active with 97% hardness has provided the highest hardness and physical activated walnut carbon active has obtained the lowest hardness value (87%). It is also found that peach activated carbon has a higher iodine number than walnut activated carbon, and this amount can be increased using chemical methods; Therefore, the highest amount of Iodine Number is related to Peach activated carbon that is made by chemical method (1230 mg/g), and the lowest amount of iodine number is seen in walnut activated carbon that is made by physical method (1020 mg/g). moreover, the pore diameter of physical activated carbon is lower than chemical activated carbon in all cases. So that the pore diameter of chemical activated peach carbon active is equal to 22.08 μm and the measured pore diameter of physical activated peach carbon active is equal to 20.42 μm. These values for walnut are obtained as 22.74 μm and 21.86 μm, respectively. Furthermore, the temperature and pH effects on the adsorption of different synthesized oily wastewater was studied and it was found that a decrease in adsorption can be seen with an increase in temperature or decreasing the pH value, which can be referred to this fact that the process of adsorption is an exothermic process. Finally, to analyze the compatibility of adsorption isotherms with experimental data and to predict the adsorption process, three different isotherms named Langmuir, Temkin, and Freundlich isotherms were applied and their parameters were correlated. The correlation results show that the Langmuir isotherm had the best correlation in all cases compared to the Freundlich and Temkin isotherms, based on the correlation coefficient, and the calculated R2 values which was greater than 0.99 in all the studied cases.

Characterization of the pristine barite mineral was established using a scanning electron microscope (SEM) and Fourier Transform Infra-Red (FTIR). Barite was applied for sodium oleate and sodium palmitate adsorption in aqueous solutions. Equilibrium adsorption data were fitted into two adsorption isotherms, three kinetic models and thermodynamic study. The concentration of the ion and pH in the solution proved to be a controlling factor in the adsorption process. Sodium oleate and sodium palmitate soaps adsorbed strongly onto the barite mineral at pH 9 and a temperature of 293k. They result was affected by the high bulk density and chemical resistance nature of barite indicated by successive increase in dosage amount. The effect of concentration and time typically gave a C-type adsorption isotherm. Adsorptive isotherm showed that sodium palmitate adsorption over natural barite was better described by the Langmuir adsorption isotherm while oleate desorption gave a good fitting with Freundlich isotherm. The adsorptive kinetics of sodium palmitate fitted well into pseudo 1 st order and 2nd order kinetics. Intra particle diffusion was not the rate-determining step. Thermodynamic study showed a physio-sorption that was exothermic. Hence the findings showed that pristine barite absorbs at optimum pH and temperature of 9 and 293K.

In the present work, activated carbon was prepared from Acacia Tortilis tree bark, utilizing phosphoric acid chemical activation, and microwave irradiation (AC-MWI). Activated carbon was also prepared by conventional phosphoric acid chemical activation and low temperature carbonization (AC-CA). Characterization of the activated carbons were performed by proximate analysis adopting ASTM standard procedures. BET-specific surface area, total ash content, bulk density, moisture content, pH, pore volume and iodine number were determined. Comparison of characteristics for both carbons, with the characteristics of AC available in the literature and commercially available in the market was performed. Comparison showed that activated carbon produced from Acacia Tortilis tree bark is well comparable with the reported characteristics of AC in literature and commercially available in market. It was found that AC-MWI has higher BET-specific surface area than AC-CA (836 m2/g and 687 m2/g respectively). Results depict that there is an increase of 22.3% in microspores component and 21.7% BET- specific surface area obtained in AC-MWI as compared to AC-CA. Similarly, the corresponding pore volume obtained (4.97 cm3/g and 4.07 cm3/g respectively) demonstrating better values as compared to the commercial ACs (<1 cm3/g). Additionally, it was found that AC can be produced by microwave irradiation in about 48.5% less time when compared to conventional low temperature heating. The adsorption study of produced ACs was performed using methylene blue as a contaminant. Study showed that MB removal rate initially increased with increase in contact time, which decreased with time until steady state was reached. Adsorption data of MB was fitted to Freundlich, Langmuir and Temkin adsorption isotherm models. All models show reasonable correlation, however, Freundlich isotherm is best to describe the MB adsorption on AC-MWI based on correlation coefficient R2 value (0.9985). The results revealed the feasibility of microwave heating for preparation of high surface area activated carbons from Acacia Tortilis tree bark.

Removal of Lead (II) from aqueous solution onto Activated carbon derived from Palm tree leaves (Phoenix dactylifera) as a novel precursor by chemical activation with ZnCl2, at specific condition of carbonization temperature at 500°C and 1 hour as a holding time and detonated as AC(PTL)ZnCl2. The obtained material was submitted to measurements of active surface area, Fourier Transform Infrared Spectroscopy (FTIR) analysis and scanning electron microscope (SEM). Batch-adsorption studied had been carried out to examine the adsorption capacity of the AC(PTL)ZnCl2 for the removal of Lead (II) from aqueous solution. The effect of various process parameters like pH, initial metal concentration, adsorbent dose, contact time, and temperature on the efficiency of Pb (II) removal was investigated. Maximum adsorption of Pb (II) on AC(PTL)ZnCl2(86.4%) was observed at pH 5.81. The optimum conditions for adsorbent dose and temperature were determined as 0.030 g and 25°C, respectively. Initial Pb (II) concentrations has important effect on AC(PTL)ZnCl2 in the studied range (25–125 mg/L) where the removal percentage increases as the metal ion decrease. The highest percentage removal of concentration corresponding to the maximum adsorption was found to be 82.75 ± 3.65. The adsorption equilibrium data was well explained by Langmuir, Freundlich and Dubinin-Radushkevich isotherm. The parameters suggested that the adsorption of Pb (II) on prepared AC(PTL)ZnCl2 is physical adsorption. The Langmuir isotherm which fitted best for the experimental data obtained showed (Correlation Coefficient, R2 = 0.9463) higher than the (Freundlich isotherm, R2 = 0.7554), but more close to (Dubinin-Radushkevich isotherm, R2 = 0.9260). The porous characteristics and adsorption efficiencies of prepared AC(PTL)ZnCl2 were also investigated.

High surface area peat moss biochar and its potential for Chromium metal adsorption from aqueous solutions

The strict new regulations to reduce the sulfur content of fuel require new economical and efficient ways to remove the sulfur from the organic sulfur components. In the current work, sulfur was removed from the actual crude oil containing 2.5 wt.% from southern Iraq, specifically the Halfaya Oil Field was studied using adsorption desulfurization with activated carbon (AC). The effects of different operating conditions, including the dose of AC (0.2-1.0 gm), time (15–120 min) and temperature (30–50°C) were investigated. The best operating conditions were obtained as 0.8 gm AC, 90 minutes and 50℃, respectively. Langmuir, Freundlich and Temkin isotherm models were implemented. The steady data were best denoted via Temkin models with correlation coefficient (R2= 0.974). The kinetics sulfur components on activated carbon were examined by using pseudo-first order, pseudo-second order kinetics models and Intra-Particle diffusion. The adsorption process can be well described by pseudo-first order adsorption kinetic model with correlation coefficient (R2 = 0.9552). Thermodynamic parameters, which include Gibbs Free Energy (ΔGo), Enthalpy (ΔHo) and Entropy (ΔSo), were determined in the present research and showed that the adsorption of sulfur components on activated carbon is spontaneous, endothermic and increases the randomness of the sulfur compounds on the surface of the adsorbent. The content of sulfur in the treated crude oil was reduced from 2.5% to 1.8% corresponding to a desulfurization efficiency of 28%.

Activated carbon prepared from cashew nut shells using potassium hydroxide activation at 850°C in N2 and CO2 atmosphere was used as an adsorbent for the removal of chromium ions from aqueous solutions. The adsorption of Cr(III) ions on activated carbon was studied. The effect of experimental parameters such as, pH of initial concentration of Cr(III) solutions, contact time, dosage of adsorbent and initial concentration of Cr(III) solutions was investigated. The Freundlich and Langmuir isotherm fitted well to data of Cr(III) adsorption. Cr(III) uptake capacity was 13.93 mg/g which was calculated from the Langmuir isotherm. Key words: Activated carbon, cashew nut shell, trivalent chromium (Cr(III)), adsorption.

Graphene oxide (GO) with high specific surface area was prepared and functionalized with ethylene diamine tetra‐acetic acid (EDTA). The as‐prepared GO and the functionalized one (GO‐EDTA) were characterized using high resolution transmission electron microscopy (HRTEM), Fourier transform infrared spectroscopy (FT‐IR), X‐ray diffraction (XRD), and Raman spectroscopy. The as‐prepared and EDTA funcationalized GO were applied as adsorbent to remove strontium(II) and cobalt(II) from water. The results indicated that the prepared materials are efficient adsorbents for strontium(II) and cobalt(II) removal. The adsorption of CoIIand SrIIunder effects of contact time, temperature, and pH was investigated It is concluded that the maximum adsorption capacities of GO for CoIIand SrIIwere about 168 and 140 mg·g–1, whereas of GO‐EDTA the values were about 197 and 158 mg·g–1, respectively. It is indicated that pH 6 and temperature 40 °C are the best condition for CoIIand SrIIremoval from water. The application of Langmuir and Freundlich isotherms indicated that Langmuir isotherm is best fit for CoIIand SrIIequilibrium adsorption. Adsorption kinetics were studied by applying pseudo first‐order, pseudo second‐order, and intraparticle diffusion models on the experimental data. The results proved that pseudo second‐order model is the best represented adsorption kinetics. Appling the intraparticle diffusion regressions on the experimental data indicated that intraparticle diffusion involved in adsorption process, which was not the only rate‐controlling step.

In this work, the adsorption of three basic dyes, namely methylene blue (MB), crystal violet (CV) and rhodamine B (RB) on the humic acid (HA) immobilized pillared clay (PILC) (HA-PILC) was studied. The adsorption capacity of dyes at 30 °C using HA–PILC was foundto be 2.6, 2.0 and 2.3 times greater than that using PILC for the removal of MB, CV and RB, respectively for an initial concentrationof 250 μmol dm-3. The adsorption process was pH dependent. The maximum dye adsorption on HA-PILC was observed at a pH of 5.0–7.0 (removal of 95.2–99.2% for MB, 92.7–97.3% for CV and 83.4–91.0% for RB) with no significant increase in removalsbeyond a pH of 7.0. The adsorption process could be best describedby the Urano and Tachikawa model showing that particle diffusion controlled adsorption. Equilibrium adsorption data were analyzed using the Langmuir, Freundlich and Redlich-Peterson isotherms. Dye adsorption was best described by the Freundlich model. The monolayer adsorption capacities of HA-PILC calculated using the Langmuir isotherm were 608.4, 484.7 and 413.1 μmol g-1 for MB, CV and RB, respectively. The linear Sheindorf-Rebhun-Sheintuch equation (Multicomponent Freundlich-type), was applied to the isotherm data obtained for each binary-solute combination of MB, CV and RB. The study showed that HA-PILC was an excellent media for the removal of basic dyes from aqueous solutions, based on adsorption kinetics and capacity.

Natural gas (NG), known for its eco-friendly energy attributes, faces challenges such as low volumetric density, leakage susceptibility, and explosion risks during storage and transport. To narrow this gap, this study reports on the potential of bio-based adsorbents from cashew nut shells (CNS) and avocado seeds (AVS) as an alternative approach for the onboard storage of NG. CNS and AVS were characterized to determine moisture content, volatile matter content, ash content, and fixed carbon content. Additionally, the study determined the optimal loading of activating agents to produce activated carbons (ACs). ACs were produced through a dual process involving simultaneous chemical activation and carbonization. In the chemical activation phase, a sample of either cashew nut shells (CNS) or avocado seeds (AVS) was impregnated with phosphoric acid at various ratios. Subsequently, the properties of the ACs, including surface area, pore volume, and X-ray diffraction (XRD), were evaluated. The NG adsorption capacity of the ACs was assessed, and Freundlich and Langmuir isotherm adsorption equations were derived to elucidate the NG adsorption behavior on the ACs. The results revealed that the proximate analysis of CNS and AVS showed low moisture content (6.48% and 8.91%), high volatile matter (80.21% and 73.09%), low ash content (1.48% and 4.71%), and high fixed carbon (13.65% and 15.59%), indicating suitability for AC formulations. During synthesis, adding phosphoric acid to AVS or CNS in a 1:1 ratio resulted in significantly larger surface areas and pore volumes in the produced ACs. X-ray diffraction analysis of the ACs produced from CNS or AVS with phosphoric acid added at a 1:1 ratio indicated a broad diffraction background and a predominantly amorphous structure. The performance of the ACs in the adsorption of NG demonstrated that ACs produced from 1:1 mixtures of CNS with phosphoric acid and AVS with phosphoric acid exhibited higher adsorption capacities, 0.038 g/g and 0.031 g/g, respectively, at a low pressure of 5 bar, showcasing a novelty of this study. Furthermore, the Freundlich equation test yielded a constant R² exceeding 0.9, with positive adsorption intensity and adsorption capacity values, indicating a favorable fit for the model. In contrast, the Langmuir equation test resulted in a constant R² exceeding 0.9, but the adsorption capacity exhibited negative values, leading to inconclusive explanations. These findings affirm that bio-wastes can be an effective source of adsorbents for onboard natural gas storage , suggesting a means to reduce the take-dispose model and promote a circular economy in the energy sector.

Adsorption of Cr3+ from aqueous solution by Rhizophora apiculata tannins was investigated in batch shaking experiments. Tannins extracted from R. apiculata mangrove barks was chemically modified with formaldehyde in the basic solution of sodium hydroxide. The performance of the produced adsorbent on the adsorption of Cr3+ was evaluated based on the effect of several parameters like initial pH, adsorbent dosage, initial Cr3+ concentration and contact time. Equilibrium adsorption data was analyzed by Langmuir, Freundlich, Sips and Dubinin-Raduskhevich (D-R) isotherms. The fitness of the isotherms to the experimental data was determined by non-linear regression analysis. Adsorption capacity calculated from Langmuir isotherm was found to be 10.14 mg Cr3+/g of adsorbent at optimum adsorption pH of 4.5. Mean energy of adsorption with the value of 10.35 kJ/mol indicated that adsorption Cr3+ on Rhizophora apiculata tannins followed ion-exchange reaction. Kinetic study showed that the adsorption process followed the pseudo second-order kinetic model. Keywords: Rhizophora apiculata, tannins, isotherms, kinetic, chromium.

An economically feasible technology for the removal of pollutants from wastewater is adsorption. Active carbon was prepared by single stage method via chemical impregnation of Pili Nut-Shell with orthophosphoric acid and activation at a temperature of 450 o C using precursor-acid ratio of 1:4 for a period of 2 h. The effects of initial concentration, contact time, adsorbent dose and pH on the uptake of 4-nitrophenol (PNP) using Pili nut-based active carbon (PAC) were determined. The PAC maximum adsorption capacity value (190.39 mg/g) was obtained at an initial concentration of 1000 mg/L and was found to be greater than that of a commercial granular active carbon, CGAC (166.97 mg/g) at an initial concentration of 800 mg/L. The BET surface area and total pore volume of PAC (960 m 2 /g, 0.422 cm 3 /g) respectively were also greater than that of CGAC (426.3 m 2 /g, 0.208 cm 3 /g). The pore size distribution of the PAC (2.842 nm) classifies it to be within range of super-microporous and as such could be used for toxic gas removal as well as small liquid molecules. The Langmuir isotherm best described the adsorption of PNP onto PAC while Pseudo second order kinetics fitted best. The adsorption process was exothermic and spontaneous. Thus, active carbon produced from Pili Nut-Shell can be used to adsorb PNP.

Electrochemical performance of activated carbons prepared from rice husk in different types of non-aqueous electrolytes

The aim of this work is to synthesize and characterize alginate-Moroccan clay bio-composite in order to improve our understanding of the adsorption of inorganic pollutants found in textile effluents. Characterization of the bio-composite used was carried out using a variety of techniques (IR-TF, SEM, DRX, and pHZPC). The influence of the medium's physico-chemical parameters (temperature, pH, initial concentration, etc.) on the retention of inorganic pollutants was also studied. Studies of adsorption and inorganic pollutants such as orthophosphate (H2PO4- and HPO42-) and nitrate (NO3-) ions were carried out, using simple solutions from the laboratory, in a batch system. This study explored the impact of adsorbent dose, contact time, solution pH, and temperature on the adsorption process. Various kinetic models, including pseudo-first-order, pseudo-second-order, intra-particle diffusion, and Elovich models, were tested and evaluated, to illustrate the adsorption kinetics. This study's findings demonstrated that the adsorption process follows second-order kinetics, with associated rate constants successfully determined. The correlation coefficient for the pseudo-second-order kinetic model is nearly equal to 1 (>0.98), and the value of theoretical adsorption capacity (qe,the) is comparable to the experimental one (qe,the = 58.14 mg/g for H2PO4-, qe,the = 54.64 mg/g for HPO42-, and qe,the = 52.63 mg/g for NO3-). Additionally, the adsorption equilibrium was investigated through the application of various mathematical models, including the Langmuir, Freundlich, Temkin, and Dubinin-Radushkevich isotherm models, to assess the mechanistic parameters associated with the adsorption process. Among these models, the Langmuir isotherm emerged as the most suitable one for characterizing the adsorption of H2PO4-, HPO42-, and NO3- ions using bio-nanocomposite beads. The maximum adsorbed amounts of metal ions by the bio-nanocomposite used were 625 mg/g for H2PO4-, 909.09 mg/g for HPO42-, and 588.23 mg/g for NO3- from the batch system. The endothermic and physical nature of the adsorption is suggested by the positive values of ΔH°, which is consistent with experimental findings. The adsorption process is spontaneous, as evidenced by the negative ΔG° values. Positive ΔS° values indicate increased randomness at the solid/liquid interface during adsorption of ion-organic ions onto the engineered bio-nanocomposite. The obtained results demonstrated that, from a scientific perspective, alginate-Moroccan clay bio-nanocomposites exhibit a highly significant adsorption capability for the removal of oxyanions in aqueous environments.

Enhanced fluoride sorption by mechanochemically activated kaolinites