Experimental investigation of adsorption capacity of anthill in the removal of heavy metals from aqueous solution

In the present work, the adsorption capacity of anthill was investigated as a low‐cost adsorbent to remove the heavy metal ions, lead (II) ion (Pb²⁺), and zinc (II) ion (Zn²⁺) from an aqueous solution. The equilibrium adsorption isotherms of the heavy metal ions were investigated under batch process. For the study we examined the effect of the solution's pH and the initial cations concentrations on the adsorption process under a fixed contact time and temperature. The anthill sample was characterized using a scanning electron microscope (SEM), X‐ray fluorescence (XRF), and Fourier transform infrared (FTIR) techniques. From the SEM analysis, structural change in the adsorbent was a result of heavy metals adsorption. Based on the XRF analysis, the main composition of the anthill sample was silica (SiO₂), alumina (Al₂O₃), and zirconia (ZrO₂). The change in the peaks of the spectra before and after adsorption indicated that there was active participation of surface functional groups during the adsorption process. The experimental data obtained were analyzed using 2‐ and 3‐parameter isotherm models. The isotherm data fitted very well to the 3‐parameter Radke–Prausnitz model. It was noted that Pb²⁺ and Zn²⁺ can be effectively removed from aqueous solution using anthill as an adsorbent.     

Adsorption characterization of Pb(II) and Cu(II) ions onto chitosan-tripolyphosphate beads: Kinetic,equilibrium and thermodynamic studies

Chitosan-tripolyphosphate (CTPP) beads were synthesized, characterized and were used for the adsorption of Pb(II) and Cu(II) ions from aqueous solution. The effects of initial pH, agitation period, adsorbent dosage, different initial concentrations of heavy metal ions and temperature were studied. The experimental data were correlated with the Langmuir, Freundlich and Dubinin-Radushkevich isotherm models. The maximum adsorption capacities of Pb(II) and Cu(II) ions in a single metal system based on the Langmuir isotherm model were 57.33 and 26.06 mg/g, respectively. However, the beads showed higher selectivity towards Cu(II) over Pb(II) ions in the binary metal system. Various thermodynamic parameters such as enthalpy (ΔH°), Gibbs free energy (ΔG°) and entropy (ΔS°) changes were computed and the results showed that the adsorption of both heavy metal ions onto CTPP beads was spontaneous and endothermic in nature. The kinetic data were evaluated based on the pseudo-first and -second order kinetic and intraparticle diffusion models. Infrared spectra were used to elucidate the mechanism of Pb(II) and Cu(II) ions adsorption onto CTPP beads.     

Immobilization of Pb(II), Cd(II) and Ni(II) ions on kaolinite and montmorillonite surfaces from aqueous medium

The present study investigates the immobilization of Pb(II), Cd(II) and Ni(II) on clays (kaolinite and montmorillonite) in aqueous medium through the process of adsorption under a set of variables (concentration of metal ion, amount of clay, pH, time and temperature of interaction). Increasing pH favours the removal of metal ions till they are precipitated as the insoluble hydroxides. The uptake is rapid with maximum adsorption being observed within 180 min for Pb(II) and Ni(II) and 240 min for Cd(II). A number of available models like the Lagergren pseudo first-order kinetics, second-order kinetics, Elovich equation, liquid film diffusion and intra-particle diffusion are utilized to evaluate the kinetics and the mechanism of the immobilization interactions. Two isotherm equations due to Langmuir and Freundlich showed good fits with the experimental data. Kaolinite and montmorillonite have considerable Langmuir monolayer capacity with respect to Pb(II), Cd(II) and Ni(II), the values being in the range of 6.8-11.5mg/g (kaolinite) and 21.1-31.1mg/g (montmorillonite). The Freundlich adsorption capacity follows a similar order. The thermodynamics of the immobilization process indicates the same to be exothermic with Pb(II) and Ni(II), but endothermic with Cd(II). The interactions with Pb(II) and Ni(II) are accompanied by decrease in entropy and Gibbs energy while the endothermic immobilization of Cd(II) is supported by an increase in entropy and an appreciable decrease in Gibbs energy. The results have established good potentiality for kaolinite and montmorillonite to remove heavy metals like Pb(II), Cd(II) and Ni(II) from aqueous medium through adsorption-mediated immobilization.     

Adsorption of basic dye from aqueous solution onto fly ash

The fly ash treated by H₂SO₄ was used as a low-cost adsorbent for the removal of a typical dye, methylene blue, from aqueous solution. An increase in the specific surface area and dye-adsorption capacity was observed after the acid treatment. The adsorption isotherm and kinetics of the treated fly ash were studied. The experimental results were fitted using Langmuir and Freundlich isotherms. It shows that the Freundlich isotherm is better in describing the adsorption process. Two kinetic models, pseudo-first order and pseudo-second order, were employed to analyze the kinetic data. It was found that the pseudo-second-order model is the better choice to describe the adsorption behavior. The thermodynamic study reveals that the enthalpy (ΔH⁰) value is positive (5.63 kJ/mol), suggesting an endothermic nature of the adsorption.     

Possible Utilization of Silica Gel Sludge for the Removal of Phenol from Aqueous Solutions: Laboratory Studies

This paper discusses the adsorption capacity of silica gel sludge for phenol removal from aqueous solution. Kinetic experiments showed that phenol adsorption was completed after 2 h. Adsorption isotherms were measured for phenol from aqueous solution onto silica gel sludge under various pHs and temperatures. Results showed that the adsorption capacities for phenol was increased as pH decreased from 6.5 to 2. Temperature also was found to affect the adsorption isotherm. As temperature increases from 30 to 50°C, the adsorption capacity increases. The adsorption equilibrium of phenol on silica gel sludge was described by the linear Freundlich and Langmuir models. Furthermore, results showed that the isotherm parameters fit both linearized Langmuir and Freundlich adsorption isotherms. The Freundlich and Langmuir parameters at optimum pH was found as K _f=2.89, 1/n=0.23 and K _d=22.0, q _m=7.98, respectively. Whereas, for those at optimum temperature it was observed as K _f=2.87, 1/n=0.16 and K _d=20.93, q _m=7.91, respectively.     

Adsorptive removal of Cd(II) and Pb(II) ions from aqueous solutions by using Turkish illitic clay

The ability of Turkish illitic clay (TIC) in removal of Cd(II) and Pb(II) ions from aqueous solutions has been examined in a batch adsorption process with respect to several experimental conditions including initial solution pH, contact time, initial metal ions concentration, temperature, ionic strength, and TIC concentration, etc. The characterization of TIC was performed by using FTIR, XRD and XRF techniques. The maximum uptake of Cd(II) (11.25 mg g⁻¹) and Pb(II) (238.98 mg g⁻¹) was observed when used 1.0 g L⁻¹ of TIC suspension, 50 mg L⁻¹ of initial Cd(II) and 250 mg L⁻¹ of initial Pb(II) concentration at initial pH 4.0 and contact time of 240 min at room temperature. The experimental data were analyzed by the Langmuir, Freundlich, Temkin and Dubinin Radushkevich (D-R) isotherm models. The monolayer adsorption capacity of TIC was found to be 13.09 mg g⁻¹ and 53.76 mg g⁻¹ for Cd(II) and Pb(II) ions, respectively. The kinetics of the adsorption was tested using pseudo-first-order, pseudo-second-order, Elovich and intraparticle diffusion models. The results showed that the adsorption of Cd(II) and Pb(II) ions onto TIC proceeds according to the pseudo-second-order model. Thermodynamic parameters including the Gibbs free energy (ΔG), enthalpy (ΔH), and entropy (ΔS) changes indicated that the present adsorption process was feasible, spontaneous and endothermic in the temperature range of 5–40 °C.     

Prediction of metal-adsorption behaviour in the remediation of water contamination using indigenous microorganisms

In recent years, the adsorption of heavy metal cations onto bacterial surfaces has been studied extensively. This paper reports the findings of a study conducted on the heavy metal ions found in mine effluents from a mining plant where Co²⁺ and Ni²⁺ bearing minerals are processed. Heavy metal ions are reported to be occasionally present in these mine effluents, and the proposed microbial sorption technique offers an acceptable solution for the removal of these heavy metals. The sorption affinity of microorganisms for metal ions can be used to select a suitable microbial sorbent for any particular bioremediation process. Interactions of heavy metal ions (Co²⁺ and Ni²⁺) and light metal ions (Mg²⁺ and Ca²⁺) with indigenous microbial cells (Brevundimonas spp., Bacillaceae bacteria and Pseudomonas aeruginosa) were investigated using the Langmuir adsorption isotherm, pseudo second-order reaction kinetics model and a binary-metal system. Equilibrium constants and adsorption capacities derived from these models allowed delineation of the effect of binding affinity and metal concentration ratios on the overall adsorption behaviour of microbial sorbents, as well as prediction of performance in bioremediation systems. Although microbial sorbents used in this study preferentially bind to heavy metal ions, it was observed that higher concentrations (>90 mg/?) of light metal ions in multi-metal solutions inhibit the adsorption of heavy metal ions to the bacterial cell wall. However, the microbial sorbents reduced Ni²⁺ levels in the mine-water used (93–100% Ni²⁺ removal) to below the maximum acceptable limit of 350 μg/?, established by the South African Bureau of Standards. Competition among metal ions for binding sites on the biomaterial surface can occur during the bioremediation process, but microbial sorption affinity for heavy metal ions can enhance their remediation in dilute (<5 mg/? heavy metal) wastewaters.     

Removal of heavy metals in rinsing wastewater from plating factory by adsorption with economical viable materials

The removal of heavy metals from plating factory wastewater with economical materials was investigated by the column method. Montmorillonite, kaolin, tobermorite, magnetite, silica gel and alumina were used as the economical adsorbents to wastewater containing Cd(II), Cr(VI), Cu(II) and Pb(II). This removal method of heavy metals proved highly effective as removal efficiency tended to increase with increasing pH and decrease with increasing metal concentration. The removal percentages by adsorption onto montmorillonite, tobermorite, magnetite, and silica gel showed high values for all metals. From the results for the heat of adsorption, the adsorption process in the present study might be chemisorption. The proposed method was successfully applied to the removal of Cd(II), Cr(VI) and Cu(II) in rinsing wastewater from plating factory in Nagoya City, Aichi Prefecture, Japan. Since the economical adsorbents used can be obtained commercially because they are easily synthesized, the wastewater treatment system developed is rapid, simple and cheap for the removal of heavy metals.     

Comparison of adsorption models in reservoir simulation of enhanced coalbed methane recovery and CO2 sequestration in coal

Coalbed methane is an important resource of energy. Meanwhile CO₂ sequestration in coal is a potential management option for greenhouse gas emissions. An attractive aspect to this process is that CO₂ is adsorbed to the coal, reducing the risk of CO₂ migration to the surface. Another aspect to this is that the injected CO₂ could displace adsorbed methane leading to enhanced coalbed methane recovery. Therefore, in order to understand gas migration within the reservoir, mixed-gas adsorption models are required. Moreover, coal reservoir permeability will be significantly affected by adsorption-induced coal swelling during CO₂ injection. Coal swelling is directly related to reservoir pressure and gas content which is calculated by adsorption models in reservoir simulation. Various models have been studied to describe the pure- and mixed-gas adsorption on coal. Nevertheless, only the Langmuir and Extended Langmuir models are usually applied in coal reservoir simulations. This paper presents simulation work using several approaches to representing gas adsorption, implemented into the coal seam gas reservoir simulator SIMED II. The adsorption models are the Extended Langmuir model (ELM), the Ideal Adsorbed Solution (IAS) model and the Two-Dimensional Equation of State (2D EOS). The simulations based on one Australian and one American coal sample demonstrated that (1) the Ideal Adsorbed Solution model, in conjunction with Langmuir model as single-component isotherm, shows similar simulation results as the ELM for both coals, with the IAS model representing the experimental adsorption data more accurately than the ELM for one coal and identically with the ELM for the other coal; (2) simulation results using the 2D EOS, however, are significantly different to the ELM or IAS model for both coal samples. The magnitude of the difference is also dependent on coal swelling and the well operating conditions, such as injection pressure.     

Loofa egyptiaca as a novel adsorbent for removal of direct blue dye from aqueous solution

In this paper, Loofa egyptiaca (LE), an agricultural plant cultivated in Egypt, was used to prepare low-cost activated carbon (LE_C1 and LE_C2) adsorbents. The adsorbents (LE, LE_C1 and LE_C2) were evaluated for their ability to remove direct blue 106 dye from aqueous solutions. Batch mode experiments were conducted using various parameters such as pH, contact time, dye concentration and adsorbent concentration. The surface chemistry of LE, LE_C1 and LE_C2 was analyzed by scanning electron microscopy (SEM). The experimental data were examined using Langmuir, Freundlich, Temkin and Harkins–Jura isotherms. The results showed that the adsorption of direct blue 106 was maximal at the lowest value of pH (pH = 2). Removal efficiency was increased with an increase in dye concentration and a decrease in amount of adsorbent. Maximum adsorption capacity was found to be 57.14, 63.3 and 73.53 mg/g for LE, LE_C1 and LE_C2 respectively. Kinetics were also investigated using pseudo-first-order, pseudo-second-order and intra-particle diffusion models. The experimental data fitted very well with the pseudo-first-order and pseudo-second-order kinetic models. The results indicate that LE, LE_C1 and LE_C2 could be employed as adsorbents for the removal of direct blue dye from aqueous solutions.     

Zeolite formation from coal fly ash and heavy metal ion removal characteristics of thus-obtained Zeolite X in multi-metal systems

Zeolitic materials have been prepared from coal fly ash as well as from a SiO₂–Al₂O₃ system upon NaOH fusion treatment, followed by subsequent hydrothermal processing at various NaOH concentrations and reaction times. During the preparation process, the starting material initially decomposed to an amorphous form, and the nucleation process of the zeolite began. The carbon content of the starting material influenced the formation of the zeolite by providing an active surface for nucleation. Zeolite A (Na-A) was transformed into zeolite X (Na-X) with increasing NaOH concentration and reaction time. The adsorption isotherms of the obtained Na-X based on the characteristics required to remove heavy ions such as Ni²⁺, Cu²⁺, Cd²⁺ and Pb²⁺ were examined in multi-metal systems. Thus obtained experimental data suggests that the Langmuir and Freundlich models are more accurate compared to the Dubinin–Kaganer–Radushkevich (DKR) model. However, the sorption energy obtained from the DKR model was helpful in elucidating the mechanism of the sorption process. Further, in going from a single- to multi-metal system, the degree of fitting for the Freundlich model compared with the Langmuir model was favored due to its basic assumption of a heterogeneity factor. The Extended-Langmuir model may be used in multi-metal systems, but gives a lower value for equilibrium sorption compared with the Langmuir model.     

Removal of copper (II) from aqueous solution by adsorption onto low-cost adsorbents

The use of low-cost adsorbents was investigated as a replacement for current costly methods of removing metals from aqueous solution. Removal of copper (II) from aqueous solution by different adsorbents such as shells of lentil (LS), wheat (WS), and rice (RS) was investigated. The equilibrium adsorption level was determined as a function of the solution pH, temperature, contact time, initial adsorbate concentration and adsorbent doses. Adsorption isotherms of Cu (II) on adsorbents were determined and correlated with common isotherm equations such as Langmuir and Freundlich models. The maximum adsorption capacities for Cu (II) on LS, WS and RS adsorbents at 293, 313 and 333 K temperature were found to be 8.977, 9.510, and 9.588; 7.391, 16.077, and 17.422; 1.854, 2.314, and 2.954 mg g(-1), respectively. The thermodynamic parameters such as free energy (delta G0), enthalpy (delta H0) and entropy changes (delta S0) for the adsorption of Cu (II) were computed to predict the nature of adsorption process. The kinetics and the factors controlling the adsorption process were also studied. Locally available adsorbents were found to be low-cost and promising for the removal of Cu (II) from aqueous solution.     

Investigating the quantitative and qualitative status of effluent in the wastewater treatment plant in Iran Central Iron Ore

The aim of present study was to investigate the quality of the produced effluent from different units of the Iran Central Iron Ore in Bafq city and comparison of effluent with the standards. This study presents the physicochemical and biological parameters data of effluent of three Sequencing batch reactors (SBR) with a capacity of 160 m³?d^?1. Most common parameters include pH, total suspended solids (TSS), total nitrogen (TN), total phosphorus (TP), biochemical oxygen demand (BOD₅), chemical oxygen demand (COD), heavy metals, and total coliforms and fecal coliforms as biological indicators. Then, for each SBR system, the average of each parameter was determined, and results were compared with the standard recommended by the Iranian Environmental Protection Agency. Based on the results, some of the parameters, including BOD₅, COD, and TSS in the wastewater treatment plant (WWTP) effluent, are higher than the permitted amount for discharge to the surface water. Considering the BOD₅, COD, and TSS concentration in WWTPs, the treated wastewater is only suitable for agricultural and irrigation use. Therefore, wastewater produced by Iran Central Iron Ore Co. will need additional treatment to achieve standard quality of water before discharge in surface water and adsorbent well.     

Biosorption of lead by maize (Zea mays) stalk sponge

This study investigated the removal of Pb(II) from aqueous solutions by a maize (Zea mays) stalk sponge. Equilibrium and kinetic models for Pb(II) sorption were developed by considering the effect of the contact time and concentration at the optimum pH of 6 ± 0.2. The Freundlich model was found to describe the sorption energetics of Pb(II) by Z. mays stalk sponge, and a maximum Pb(II) loading capacity of 80 mg g^?1 was determined. The kinetic parameters were obtained by fitting data from experiments measuring the effect of contact time on adsorption capacity into pseudo-first and second-order equations. The kinetics of Pb(II) sorption onto Z. mays biosorbent were well defined using linearity coefficients (R²) by the pseudo-second-order equation (0.9998). The results obtained showed that Zea may stalk sponge was a useful biomaterial for Pb(II) sorption and that pH has an important effect on metal biosorption capacity.     

Biosorption of copper(II) and lead(II) onto potassium hydroxide treated pine cone powder

Pine cone powder surface was treated with potassium hydroxide and applied for copper(II) and lead(II) removal from solution. Isotherm experiments and desorption tests were conducted and kinetic analysis was performed with increasing temperatures.As solution pH increased, the biosorption capacity and the change in hydrogen ion concentration in solution increased. The change in hydrogen ion concentration for lead(II) biosorption was slightly higher than for copper(II) biosorption. The results revealed that ion-exchange is the main mechanism for biosorption for both metal ions. The pseudo-first order kinetic model was unable to describe the biosorption process throughout the effective biosorption period while the modified pseudo-first order kinetics gave a better fit but could not predict the experimentally observed equilibrium capacities. The pseudo-second order kinetics gave a better fit to the experimental data over the temperature range from 291 to 347 K and the equilibrium capacity increased from 15.73 to 19.22 mg g^?1 for copper(II) and from 23.74 to 26.27 for lead(II).Activation energy was higher for lead(II) (22.40 kJ mol^?1) than for copper(II) (20.36 kJ mol^?1). The free energy of activation was higher for lead(II) than for copper(II) and the values of ΔH* and ΔS* indicate that the contribution of reorientation to the activation stage is higher for lead(II) than copper(II). This implies that lead(II) biosorption is more spontaneous than copper(II) biosorption.Equilibrium studies showed that the Langmuir isotherm gave a better fit for the equilibrium data indicating monolayer coverage of the biosorbent surface. There was only a small interaction between metal ions when simultaneously biosorbed and cation competition was higher for the Cu-Pb system than for the Pb-Cu system. Desorption studies and the Dubinin–Radushkevich isotherm and energy parameter, E, also support the ion-exchange mechanism.     

Adsorption of Pb and Cd on the natural surface coatings (NSCs) in the presence of organochlorine pesticides: a preliminary investigation

Adsorption of Pb and Cd in the presence and absence of organochlorine pesticides (OCPs) on natural surface coatings (NSCs), which were collected in the Nanhu Lake in Changchun, China, was measured in order to investigate the effect of the OCPs on the adsorption of heavy metals on the NSCs. Adsorption of Pb/Cd was carried out under controlled laboratory conditions (mineral salt solution with defined species, ionic strength 0.05 mol/l, 25 degrees C and pH 6.0) with initial Pb and Cd concentrations ranging from 0.2 to 2.5 mol/l. The classical Langmuir adsorption isotherm was applied to estimate the equilibrium coefficients of the adsorption of Pb and Cd on the NSCs. Adsorption interference between Pb/Cd and the OCPs on the NSCs indicated that the adsorption of Pb/Cd on the NSCs was influenced by the OCPs, and competitive adsorption between Pb and the OCPs was observed while adsorption of Cd was enhanced by addition of the OCPs. Adsorption data fit the Langmuir isotherm well for the NSCs treated with the OCPs at different equilibrium concentrations. The results showed that the amount of adsorbed Pb decreased by more than 40% while the amount of adsorbed Cd increased by over 60% with an increase in the initial concentrations of the OCPs ranging from 0 to 5.0 microg/l and that adsorption of Pb/Cd on the NSCs was strongly affected by the OCPs. This preliminary study highlights the importance of the OCPs on the NSCs in controlling the transport, fate, biogeochemistry, bioavailability and toxicity of trace metals in aquatic environments.     

Health risk assessment due to heavy metal exposure from commonly consumed fish and vegetables

Contamination of heavy metals in fish and vegetables is regarded as a major crisis globally, with a large share in many developing countries. In Bogra District of Bangladesh, concentrations of six heavy metals, i.e., chromium (Cr), nickel (Ni), copper (Cu), arsenic (As), cadmium (Cd) and lead (Pb), were evaluated in the most consumed vegetables and fish species. The sampling was conducted during February–March 2012 and August–September 2013. The levels of metals varied between different fish and vegetable species. Elevated concentrations of As, Cd and Pb were observed in vegetable species (Solanum tuberosum, Allium cepa and Daucus carota), and fish species (Anabas testudineus and Heteropneustes fossilis) were higher than the FAO/WHO permissible limits, indicating these three metals might pose risk from the consumption of these vegetable and fish species. The higher concentration of heavy metals in these vegetable species might be due to the higher uptake from soil and sediment ingestion behavior in fish species. Multivariate principal component analysis (PCA) showed significant anthropogenic contributions of Cr, Ni, Cu and Pb in samples as the PCA axis scores were correlated with scores of anthropogenic activities. Target hazard quotients showed that the intakes of Cu, As and Pb through vegetables and fish were higher than the recommended health standards, indicated non-carcinogenic risk. Therefore, intakes of these elements via fish and vegetables for Bangladeshi people are a matter of concern.     

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.     

Adsorption characteristics of Cu and Ni on Irish peat moss

Peat has been widely used as a low cost adsorbent to remove a variety of materials including organic compounds and heavy metals from water. Various functional groups in lignin allow such compounds to bind on active sites of peat. The adsorption of Cu(2+) and Ni(2+) from aqueous solutions on Irish peat moss was studied both as a pure ion and from their binary mixtures under both equilibrium and dynamic conditions in the concentration range of 5-100mg/L. The pH of the solutions containing either Cu(2+) or Ni(2+) was varied over a range of 2-8. The adsorption of Cu(2+) and Ni(+2) on peat was found to be pH dependent. The adsorption data could be fitted to a two-site Langmuir adsorption isotherm and the maximum adsorption capacity of peat was determined to be 17.6 mg/g for Cu(2+) and 14.5mg/g for Ni(2+) at 298 K when the initial concentration for both Cu(2+) and Ni(2+) was 100mg/L, and the pH of the solution was 4.0 and 4.5, respectively. Column studies were conducted to generate breakthrough data for both pure component and binary mixtures of copper and nickel. Desorption experiments showed that 2mM EDTA solution could be used to remove all of the adsorbed copper and nickel from the bed.     

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.