Optimization of activated carbon production from empty fruit bunch fibers in one-step steam pyrolysis for cadmium removal from aqueous solution

The fast growth of the palm oil industry in Malaysia is associated with various waste products, namely the empty fruit bunches (EFB), which have a negative impact on the environment. Therefore, these wastes were utilized as a cheap raw material for the production of activated carbon (AC) with less energy consumption. One-step steam pyrolysis was used to produce AC from oil palm empty fruit bunch fibers (EFBF) by varying the operating parameters of temperature, steam flow rate, and activation time using two-level full factorial experimental design (FFD). Ten samples of AC were prepared and the optimized production conditions were chosen based on the ability to adsorb and remove cadmium. Physical activation comprised of carbonization for 30 min using nitrogen gas (N₂), followed by activation with steam at different flow rates (2.0, 3.0, and 4.0 ml/min), temperatures (600, 750, and 900°C) and times (15, 30, and 45 min). The AC sample produced at an activation temperature of 900°C with a steam flow rate of 2.0 ml/min and activation time of 15 min was selected as the best adsorbent with a total yield of 21.7%. It had adsorbed more than 97% of total cadmium from aqueous solution within 2 min of the contact time. Characterization of EFBF-based AC by SEM and BET surface area analysis had shown a good-quality adsorbent with highly active sites and well-developed pores with BET surface area of 635.16 m²/g. Experimental results indicated that the prepared AC from EFBF provide a promising solution in water and wastewater treatment.     

Batch sorption dynamics and equilibrium for the removal of lead ions from aqueous phase using activated carbon developed from coffee residue activated with zinc chloride

Lignocellulosic materials are good precursors for the production of activated carbon. In this work, coffee residue has been used as raw material in the preparation of powder activated carbon by the method of chemical activation with zinc chloride for the sorption of Pb(II) from dilute aqueous solutions.The influence of impregnation ratio (ZnCl₂/coffee residue) on the physical and chemical properties of the prepared carbons was studied in order to optimize this parameter. The optimum experimental condition for preparing predominantly microporous activated carbons with high pore surface area (890 m²/g) and micropore volume (0.772 cm³/g) is an impregnation ratio of 100%. The developed activated carbon shows substantial capability to sorb lead(II) ions from aqueous solutions and for relative impregnation ratios of 75 and 100%, the maximum uptake is practically the same. Thus, 75% represents the optimal impregnation ratio.Batch experiments were conducted to study the effects of the main parameters such as contact time, initial concentration of Pb(II), solution pH, ionic strength and temperature. The maximum uptake of lead(II) at 25 °C was about 63 mg/g of adsorbent at pH 5.8, initial Pb(II) concentration of 10 mg/L, agitation speed of 200 rpm and ionic strength of 0.005 M. The kinetic data were fitted to the models of pseudo-first order and pseudo-second order, and follow closely the pseudo-second order model. Equilibrium sorption isotherms of Pb(II) were analyzed by the Langmuir, Freundlich and Temkin isotherm models. The Freundlich model gives a better fit than the others.Results from this study suggest that activated carbon produced from coffee residue is an effective adsorbent for the removal of lead from aqueous solutions and that ZnCl₂ is a suitable activating agent for the preparation of high-porosity carbons.     

Magnetic composite prepared from palm shell-based carbon and application for recovery of residual oil from POME

Magnetic separation combined with adsorption by activated carbon has been found to be a useful method for removing pollutants. In this paper, the use of palm shell as a source of activated carbon for the removal and recovery of oil from palm oil mill effluent (POME) is studied. In the first part of the study, the properties of samples of activated carbon prepared from palm shell under a variety of different conditions were characterized for their hydrophobicity, surface areas and pore size distribution. The most effective of the activated carbon samples was prepared by impregnation with ZnCl(2) followed by combined physical/chemical activation under carbon dioxide flow at 800 °C. Four grams of these samples adsorbed 90% of the oil from 50 mL POME. In the second part, the palm shell-based carbon samples were given magnetic properties by the technique of iron oxide deposition. Ninety-four percent of the activated carbon/iron oxide composite containing the adsorbed oil could be extracted from the POME by a magnetic bar of 0.15 T. Four grams of the composite can remove 85% of oil from 50 mL POME and a total of 67% of the initial oil can then be recovered by hexane extraction. Powder X-ray diffractometry showed the presence of magnetite and maghemite in the activated carbon/iron oxide composite.     

Conversion of leather wastes to useful products

The main objective of the present study is to investigate the production of useful materials from different kinds of leather waste. Three different types of tannery wastes (chromium- and vegetable-tanned shavings, and buffing dust) were pyrolyzed in a fixed bed reactor at temperatures of 450 and 600 °C under N₂ atmosphere. Gas, oil, ammonium carbonate and carboneous residue were obtained by pyrolysis. The effect of temperature and type of leather waste on product distribution of pyrolysis was investigated. Buffing dust gave the highest yield of oil (ca. 23%), while other wastes recorded yields of ca. 9%. Results of elemental analysis and column chromatography showed that pyrolysis oils could be used as fuel or chemical feedstock after re-treatment. The yields of carboneous residue (chars) were between 37.5% and 48.5% and their calorific value was between 4300 and 6000 kcal kg⁻¹, suitable for use as solid fuel. In addition, these chars were activated by CO₂ to obtain the activated carbon. The activated carbon having highest surface area (799.5 m² g⁻¹) was obtained from chromium-tanned shavings. Activated carbons prepared from chromium-tanned leather were presented as an adsorbant for the adsorption of dyes from aqueous solution.     

Preparation and characterization of activated carbon from a new raw lignocellulosic material: Flamboyant (Delonix regia) pods

Activated carbons were prepared from flamboyant pods by NaOH activation at three different NaOH:char ratios: 1:1 (AC-1), 2:1 (AC-2), and 3:1 (AC-3). The properties of these carbons, including BET surface area, pore volume, pore size distribution, and pore diameter, were characterized from N₂ adsorption isotherms. The activated carbons obtained were essentially microporous and had BET surface area ranging from 303 to 2463 m² g⁻¹.¹³C (CP/MAS and MAS) solid-state NMR shows that the lignocellulosic structures were completely transformed into a polycyclic material after activation process, thermogravimetry shows a high thermal resistance, Boehm titration and Fourier-transform infrared spectroscopy allowed characterizing the presence of functional groups on the surface of activated carbons. Scanning electron microscopy images showed a high pore development. The experimental results indicated the potential use of flamboyant pods as a precursor material in the preparation of activated carbon.     

Dry reforming of methane over oil palm shell activated carbon and ZSM-5 supported cobalt catalysts

In this study, cobalt supported oil palm shell activated carbon (Co/OPS-AC) and ZSM-5 zeolite (Co/ZSM-5) catalysts have been prepared for dry reforming of methane. Cobalt ratios of 6.0 and 14.0 wt% were deposited via wet impregnation method to the OPS-AC and ZSM-5 catalysts. The catalysts were characterized by XRD, N₂ adsorption--desorption isotherms, BET surface area, SEM, FESEM-EDX, TPR-H₂, and TPD-NH₃. The dry reforming of methane was performed using a micro reactor system under the condition of 10,000 ml/h.g-cat, 3 atm, CH₄/CO₂ ratio of 1.2:1.0 and temperature range from 923 K to 1023 K. The gaseous products were analyzed by gas chromatography (GC) with thermal conductivity detector (TCD) and further quantified to determine the conversions of CH₄ and CO₂, and the yields of CO and H₂. Experimental results revealed both catalysts exhibited lower conversions of CO₂ and CH₄ with the increase in temperature from 923 K to 1023 K. The reduced conversions may be due to the formation of carboneous substance on the catalyst known as coking. Comparatively, Co/OPS-AC gave higher conversions of CO₂ and CH₄ as well as higher yields of H₂ and CO as it has a higher surface area than Co/ZSM-5 which subsequently rendered higher activity for the reforming of methane. With the increasing cobalt loadings and reaction temperature, OPS-AC(14) catalyst exhibited improved activity and H₂/CO ratio. Based on these results, cobalt supported OPS activated carbon catalyst was suggested to be more effective for CO₂ and CH₄ conversions.     

Use of an activated carbon from antibiotic waste for the removal of Hg(II) from aqueous solution

Porous carbon has been prepared from waste antibiotic material by a chemical activation method using K(2)CO(3) as an activating reagent. Carbon was studied systematically by the adsorption of nitrogen and iodine. It was found that the process parameters such as activation temperature and activation time are crucial for preparing high-quality activated carbon. The proper choice of the preparation conditions allows to produce microporous activated carbon with a micropore volume up to 0.492 cm(3)/g and a BET surface area of 1260 m(2)/g. Adsorption of mercury(II) from an aqueous solution on antibiotic carbon was investigated under the varying conditions of agitation time, metal ion concentration and pH. The adsorption capacity of the carbon is 129 mg/g.     

Equilibrium studies of copper ion adsorption onto palm kernel fibre

The equilibrium sorption of copper ions from aqueous solution using a new adsorbent, palm kernel fibre, has been studied. Palm kernel fibre is obtained in large amounts as a waste product of palm oil production. Batch equilibrium studies were carried out and system variables such as solution pH, sorbent dose, and sorption temperature were varied. The equilibrium sorption data was then analyzed using the Langmuir, Freundlich, Dubinin–Radushkevich (D–R) and Temkin isotherms. The fit of these isotherm models to the equilibrium sorption data was determined, using the linear coefficient of determination, r², and the non-linear Chi-square, χ² error analysis.The results revealed that sorption was pH dependent and increased with increasing solution pH above the pH_PZC of the palm kernel fibre with an optimum dose of 10 g/dm³. The equilibrium data were found to fit the Langmuir isotherm model best, with a monolayer capacity of 3.17 × 10^?4 mol/g at 339 K. The sorption equilibrium constant, K_a, increased with increasing temperature, indicating that bond strength between sorbate and sorbent increased with temperature and sorption was endothermic. This was confirmed by the increase in the values of the Temkin isotherm constant, B₁, with increasing temperature. The Dubinin–Radushkevich (D–R) isotherm parameter, free energy, E, was in the range of 15.7–16.7 kJ/mol suggesting that the sorption mechanism was ion exchange. Desorption studies showed that a high percentage of the copper was desorbed from the adsorbent using acid solutions (HCl, HNO₃ and CH₃COOH) and the desorption percentage increased with acid concentration. The thermodynamics of the copper ions/palm kernel fibre system indicate that the process is spontaneous and endothermic.     

Application of sludge-based carbonaceous materials in a hybrid water treatment process based on adsorption and catalytic wet air oxidation

This paper describes a preliminary evaluation of the performance of carbonaceous materials prepared from sewage sludges (SBCMs) in a hybrid water treatment process based on adsorption and catalytic wet air oxidation; phenol was used as the model pollutant. Three different sewage sludges were treated by either carbonisation or steam activation, and the physico-chemical properties of the resultant carbonaceous materials (e.g. hardness, BET surface area, ash and elemental content, surface chemistry) were evaluated and compared with a commercial reference activated carbon (PICA F22). The adsorption capacity for phenol of the SBCMs was greater than suggested by their BET surface area, but less than F22; a steam activated, dewatered raw sludge (SA_DRAW) had the greatest adsorption capacity of the SBCMs in the investigated range of concentrations (<0.05 mol L^?1). In batch oxidation tests, the SBCMs demonstrated catalytic behaviour arising from their substrate adsorptivity and metal content. Recycling of SA_DRAW in successive oxidations led to significant structural attrition and a hardened SA_DRAW was evaluated, but found to be unsatisfactory during the oxidation step. In a combined adsorption–oxidation sequence, both the PICA carbon and a selected SBCM showed deterioration in phenol adsorption after oxidative regeneration, but a steady state performance was reached after 2 or 3 cycles.     

Direct utilization of kitchen waste for bioethanol production by separate hydrolysis and fermentation (SHF) using locally isolated yeast

Kitchen wastes containing high amounts of carbohydrates have potential as low-cost substrates for fermentable sugar production. In this study, enzymatic saccharification of kitchen waste was carried out. Response surface methodology (RSM) was applied to optimize the enzymatic saccharification conditions of kitchen waste. This paper presents analysis of RSM in a predictive model of the combined effects of independent variables (pH, temperature, glucoamylase activity, kitchen waste loading, and hydrolysis time) as the most significant parameters for fermentable sugar production and degree of saccharification. A 100 mL of kitchen waste was hydrolyzed in 250 mL of shake flasks. Quadratic RSM predicted maximum fermentable sugar production of 62.79 g/L and degree of saccharification (59.90%) at the following optimal conditions: pH 5, temperature 60°C, glucoamylase activity of 85 U/mL, and utilized 60 g/L of kitchen waste as a substrate at 10 h hydrolysis time. The verification experiments successfully produced 62.71 ± 0.7 g/L of fermentable sugar with 54.93 ± 0.4% degree of saccharification within 10 h of incubation, indicating that the developed model was successfully used to predict fermentable sugar production at more than 90% accuracy. The sugars produced after hydrolysis of kitchen waste were mainly attributed to monosaccharide: glucose (80%) and fructose (20%). The fermentable sugars obtained were subsequently used as carbon source for bioethanol production by locally isolated yeasts: Saccharomyces cerevisiae, Candida parasilosis, and Lanchancea fermentati. The yeasts were successfully consumed as sugars hydrolysate, and produced the highest ethanol yield ranging from 0.45 to 0.5 g/g and productivity between 0.44 g L^–1 h^–1 and 0.47 g L^–1 h^–1 after 24-h incubation, which was equivalent to 82.06–98.19% of conversion based on theoretical yield.     

Removal of polycyclic aromatic hydrocarbons from aqueous solution on soybean stalk-based carbon

Soybean [ (L.) Merr.] stalk-based carbons were prepared by phosphoric acid activation at different carbonization temperatures. Characteristics of the prepared carbon, including specific surface area, iodine number, and amount of methylene blue sorption, were determined. Experiments on phenanthrene, naphthalene, and acenaphthene, as representatives of polycyclic aromatic hydrocarbons (PAHs), removal from aqueous solution by the prepared carbon were conducted at different levels of carbon addition. The results indicated that the specific surface area, iodine number, and amount of methylene blue sorption increased with an increase of carbonization temperature. The maximum values were observed at 700°C and were 287.63 m g, 508.99 mg g, and 90.14 mg g, respectively. The removal efficiencies of phenanthrene, naphthalene, and acenaphthene tended to increase with increasing carbon amounts and carbonization temperature. The optimal removal performance was obtained under the experimental conditions of carbon concentrations of 0.04 g 32 mL and carbonization temperature of 700°C, and the removal efficiencies of phenanthrene, naphthalene, and acenaphthene were 99.89, 100, and 95.64%, respectively. The performance of the prepared carbon was superior to that of commercial activated carbon. Additionally, for the same carbon concentrations, the removal efficiency of PAHs on prepared carbons followed the order: phenanthrene > naphthalene > acenaphthene. Results obtained from this work provide some insight into the reuse of an agricultural residue, and also provide a new application for the treatment of PAHs in contaminated water utilizing activated carbon prepared from agricultural residues.     

CARBON CONTENT OF SEDIMENTS OF SMALL RESERVOIRS1

ABSTRACT: Carbon content was measured in sediments deposited in 58 small reservoirs across the United States. Reservoirs varied from 0.2 to 4000 km2 in surface area. The carbon content of sediment ranged from 0.3 to 5.6 percent, with a mean of 1.9 ± 1.1 percent. No significant differences between the soil and sediment carbon content were found using a paired t-test or ANOVA. The carbon content of sediments in reservoirs was similar to the carbon content of surface soils (0–10 cm) in the watershed, except in watersheds with shrub or steppe (desert) vegetation. Based on the sediment accumulation rates measured in each reservoir, the calculated organic carbon accumulation rates among reservoirs ranged from 26 to 3700 gC m^-2yr^-1, with a mean of 675 ± 739 gC m^-2yr^-1. The carbon content and accumulation rates were highest in sediments from grassland watersheds. High variability was found in carbon content, carbon accumulation, and sediment accumulation rates due to individual watershed and reservoir characteristics rather than to any broad physiographic patterns. The carbon accumulation rates in these reservoir sediments indicate that reservoir sediments could be a significant sink for organic carbon.     

Kinetic studies on the adsorption of phenol, 4-chlorophenol,and 2,4-dichlorophenol from water using activated carbons

This study uses rate parameters in pseudo-first-order (PFO) and pseudo-second-order (PSO) equations (k₁ and k₂q_e, respectively) to judge the extent for approaching equilibrium in an adsorption process. Out of fifty-six systems collected from the literature, the adsorption processes with a k₂q_e value between 0.1 and 0.8 min^?1 account for as much as 70% of the total. These are classified as fast processes. This work compares the validity of PFO and PSO equations for the adsorption of phenol, 4-chlorophenol (4-CP), and 2,4-dichlorophenol (2,4-DCP) on activated carbons prepared from pistachio shells at different NaOH/char ratios. The activated carbons, recognized as microporous materials, had a surface area ranging from 939 to 1936 m²/g. Findings show that the adsorption of phenol, 4-CP, and 2,4-DCP on activated carbons had a k₂q_e value of 0.15–0.58 min^?1, reflecting the fast process. Evaluating the operating time by rate parameters revealed that k₂q_e was 1.6–1.8 times larger than k₁. These findings demonstrate the significance of using an appropriate kinetic equation for adsorption process design.     

Assessment of soil erosion under rainfed sugarcane in KwaZulu‐Natal,South Africa

Soil erosion from agricultural land use runoff is a major threat to the sustainability of soil composition and water resource integrity. Sugarcane is an important cash and food security crop in South Africa, subjected to an intensive soil erosion, and consequently, severe land degradation. This study aimed to investigate soil erosion and associated soil and cover factors under rainfed sugarcane, in a small catchment, KwaZulu‐Natal, South Africa. Three replicated runoff plots were installed at different slope positions (down, mid and upslope) within cultivated sugarcane fields to monitor soil erosion during the 2016–2017 rainy season. On average, annual runoff (RF) was significantly greater from 10 m² plots with 1163.77 ± 2.63 l/m/year compared to 1 m² plots. However, sediment concentration (SC) was significantly lower in 10 m² (0.34 ± 0.04 g/l) compared to 1 m² (6.94 ± 0.24 g/l) plots. The annual soil losses (SL) calculated from 12 rainfall events was 58.36 ± 0.77 and 8.84 ± 0.20 t/ha from 1 m² and 10 m² plots, respectively. The 1 m² plot, SL (2.4 ± 1.41 ton/ha/year) in the upslope experienced 33% more loss than the midslope and 50% more loss than the downslope position. SL was relatively lower from the 10 m² plots than the 1 m² plots, which is explained by high sediment deposition at the greater plot scale. SL was negatively correlated with the soil organic carbon stocks (r = ?0.82) and soil surface cover (r = ?0.55). RF decreased with the increase of slope gradient (r = ?0.88) and soil infiltration rate (r = ?0.87). There were considerable soil losses from cultivated sugarcane fields with low organic matter. These findings suggest that to mitigate soil erosion, soil organic carbon stocks and vegetation cover needs to be increased through appropriate land management practices, particularly in cultivated areas with steep gradients.     

Preparation of activated carbons from unburnt coal in bottom ash with KOH activation for liquid-phase adsorption

In this work, unburnt coal (UC) in bottom ash from coal-fired power plants was soaked in KOH solution and activated for 1 h at 780 °C. The yield of activated carbons varied from 47.8 to 54.8% when the KOH/UC weight ratio changed from 2 to 4. Pore properties of these activated carbons including the BET surface area, pore volume, pore size distribution, and pore diameter were characterized based on N₂ adsorption isotherms. It was shown that the isotherms for the adsorption of methylene blue, acid blue 74, and 4-chlorophenol from aqueous solutions on these activated carbons at 30 °C were well fitted by the Langmuir equation (correlation coefficient r² > 0.9968). The adsorption capacities of methylene blue, acid blue 74, and 4-chlorophenol were obtained to be 2.40–2.88, 0.57–1.29, and 2.34–5.62 mmol/g, respectively. Moreover, the adsorption kinetics could be suitably described by the Elovich equation.     

Organic carbon diminution and estimates of carbon dioxide release from plantation soil

Summary This paper evaluates the rates of organic carbon diminution in the soil under monospecific tree plantations of teak, gmelina, rubber, oil palm, cashew and coffee. The differences between the organic carbon status of their soils and soil under nearby natural rain forest vegetation are compared. Annual rates of organic carbon decrease for the 0–10 cm soil layer, varied from 82.1 kg ha^–1 for cashew to 316.7 kg ha^–1 for oil palm. The tree plantations appear to release more carbon dioxide from the soil into the atmosphere than the natural forest. They therefore, appear to have the potential of contributing towards global warming — a threat they are supposed to mitigate.     

Fabrication and characterization of electrospun porous cellulose acetate nanofibrous mats incorporated with capric acid as form-stable phase change materials for storing/retrieving thermal energy

Electrospun cellulose acetate (CA) nanofibrous mats incorporated with capric acid was studied to fabricate form-stable phase change materials (PCMs) for storing/retrieving thermal energy. Electrospun CA nanofibrous mats with different porous structures and specific surface areas were firstly prepared through regulating the volume ratio of mixture solvent of acetone/dichloromethane (DCM). Effects of different volume ratio of mixture solvent and mat thickness on the morphological structure, specific surface area, and absorption capacity of CA nanofibrous mats were systematically investigated. The results indicated that CA nanofibrous mats were highly porous on the surface; hence, they were capable of absorbing a large amount of capric acid. The maximum absorption capacity of CA mats via electrospinning with volume ratio of acetone/DCM being 5/5 was ~95.8 wt%, due to its higher specific surface area of ~17.1 m²/g. The specific surface area and capric acid absorption capacity of CA nanofibrous mats increased with the increases of mat thickness. As the thickness of nanofibrous mats increased from 10 to 85 μm, the corresponding specific surface area and capric acid absorption capacity of mats increased respectively from 7.2 to 29.0 m²/g and 92.1 to 98.5%. Morphological structures, as well as the properties of thermal energy storage and thermal insulation of the fabricated form-stable PCMs, were studied by scanning electron microscopy, differential scanning calorimetry, and measurement of freezing times, respectively. The results indicated that the resulting form-stable PCMs could well maintain their phase transition characteristics and demonstrated great thermal energy storage capability and temperature regulation ability.     

Industry to Industry By-products Exchange Network towards zero waste in palm oil refining processes

This paper presents a systematic framework for optimal utilization of by-products generated during crude palm oil refining processes. Three by-products are considered in the supply chain network: soapstock, palm fatty acid distillate (PFAD) and spent bleaching earth (SBE). These by-products, generated from neutralization, deodorization and bleaching processes, are viable feedstocks to other commercial industries such as animal feed, biodiesel, lubricant and soap. The case study is formulated as Mixed Integer Linear Programming (MILP) and integrated into the framework with the objective to maximize the refinery's profit as well as moving towards a conscious mindset of zero waste. This is the first time that such framework is developed and applied for the palm oil industry. The framework is called as Industry to Industry By-products Exchange Network (I2IBEN). An illustrative case study demonstrates a significant potential profit of MYR182, 893 per month.     

ALGAL BIOASSAY AND GROSS PRODUCTIVITY EXPERIMENTS USING SEWAGE EFFLUENT IN A MICHIGAN WETLAND'

ABSTRACT: One component of the filamentous algal community of a northern fen ecosystem in central Michigan was studied under conditions of nutrient enrichment by secondarily treated sewage effluent during one growing season. The productivity of Cladophora spp. measured by continuous flow bioassay was 2.6 g dry weight m day at the site of effluent addition compared to 0.085 g m day at the control site. Under conditions of nutrient enrichment, uptake by bioassay Cladophora spp. averaged 12 mg m^?2day^?1for phosphorus and 55 mg m^?2day^?1for nitrogen, compared to 0.01 mg m^?2 day^?1and 0.16 mg m^?2day^?1for phosphorus and nitrogen, respectively, in the control area. At the end of the growing season approximately 4.3 g N m^?2 and 0.96 g P m^?2were immobilized in Cladophora algal biomass. Algal growth temporarily immobilized 3.0 percent of the nitrogen and 1.0 percent of the phosphorus added as sewage effluent. Gross productivity of surface water in the fen averaged 1.5 g O₂m^?2day^?1at the nutrient enriched site, compared to 0.5 g O₂ m^?2day^?1at the control area. Gross productivity, community respiration and reaeration constant values in the fen were similar to data collected by other researchers in shallow water aquatic systems, but only at the fertilized sites.     

Adsorption of carbon dioxide using impregnated activated carbon promoted by Zinc

The effect of impregnation of activated carbon with Cr₂O and Fe₂O₃ and promotion by Zn²⁺ on its adsorptive properties of carbon dioxide was studied using a volumetric adsorption apparatus at ambient temperature and low pressures. Slurry and solution impregnation methods were used to compare CO₂ capture capacity of the impregnated activated carbon promoted by Zinc. The obtained adsorption isotherms showed that amount of CO₂ adsorbed on the samples impregnated by Cr₂O was increased about 20% in compare to raw activated carbon. The results also showed that Fe₂O₃ was not an effective impregnating species for activated carbon modification. Moreover slurry impregnation method showed higher CO₂ adsorption capacity in comparison with solution impregnation method. Samples prepared by co-impregnation of two metal species showed more adsorption capacity than samples impregnated by just one metal species individually. Washing the impregnated samples by metal oxide resulted in 15% increase in CO₂ adsorption capacities of activated carbons which can be attributed to the metal oxides removal covering the adsorption surface. Decreasing impregnation temperature from 95 to 25 °C in solution method showed a significant increase in CO₂ adsorption capacity. Sips equation was found a suitable model fitting to the adsorption data in the range studied.