Batch Adsorption Process Research Articles

Assessment of Modified Rice Husks for Removal of Aniline in Batch Adsorption Process: Optimization and Isotherm Study

Assessment of Modified Rice Husks for Removal of Aniline in Batch Adsorption Process: Optimization and Isotherm Study

Evaluation of surface phenomena of magnetic biomass for dye removal via surface modeling

Methylene blue (MB) dye is used in various industries; however, it is detrimental to both humans and the environment. This study reports on the adsorptive removal of methylene blue (MB) using a magnetically modified agro-waste: iron oxide loaded Lonicera japonica flower powder (IOLJF). The interaction effects of operating variables such as the initial MB concentration, temperature, dosage of IOLJF, and pH on the IOLJF removal efficiency for MB were investigated systematically and statistically. The results showed that the adsorptive removal of MB was explained well by the pseudo-second-order (PSO) kinetic model and the Langmuir and Freundlich isotherms. The maximum uptake capacity was 403.44 mg/g at pH 6.0 and 293 K. The MB adsorption process was complex on the surface of the IOLJF. To comprehend the essential characteristics and envision the removal efficiency in the batch adsorption process, two approaches were used, namely the response surface methodology (RSM) and the data-driven adaptive neuro-fuzzy inference system (ANFIS). The RSM (R2 = 0.9782) and ANFIS (R2 = 0.9964) model predictions were both good and comparable with the experimental data. Further, it was found that the magnetic biomass could be re-used for up to seven cycles without losing its efficacy of ~95%. Overall, the results indicated that the IOLJF had sufficient potential for wastewater treatment.

Incorporation of lanthanum particles to polyethersulfone ultrafiltration membrane for specific phosphorus uptake: Method comparison and performance assessment

It is known that phosphorus is a major contributor to the occurrence of eutrophication. As such, it is of importance to remove it from water. Nanofiltration (NF) has low phosphorus selectivity and requires a relatively high pressure to achieve the separation, though it is capable of removing phosphorus. In this paper, we report our findings of method development on fabrication and application of a lanthanum (La)-incorporated polyethersulfone (PES)/sulfonated polyphenylenesulfone membrane for phosphorus treatment. The performances of membranes fabricated by the in situ and ex situ methods were examined in a series of batch adsorption and dead-end filtration experiments. The membrane fabricated by the in situ method demonstrated higher adsorption capacity (48.0 mg/g), faster kinetics (equilibrium in 6 h) and higher water permeance (>100 LMH/bar), which outperformed that by the ex situ method. Furthermore, the PES/La (in situ) membrane showed a comparable phosphate removal with a much higher permeance (about 20 times) than the NF90 (a nanofiltration commercial membrane). Moreover, the multiple cycles of filtration study showed that the membrane was reused satisfactorily in treating low-phosphate contaminated water and meeting the stringent phosphate standard limit of 0.15 mg/L. The removal of phosphate by the membranes was attributed to the mechanisms of ion exchange and electrostatic attraction/complexation. The study reported here provides a better approach in fabrication of functionalized membrane for water treatment, such as phosphate removal in either batch adsorption or membrane filtration process.

Mangosteen Peel-Derived Hydrochar Prepared via Hydrothermal Carbonization for Methylene Blue Removal

Hydrothermal carbonization (HTC) arises as an improved carbonization step developed to enhance the carbon porosity and reduce the production cost by thermally treating feedstock under milder operating conditions. This work aimed to generate hydrochar from mangosteen peel (MPHTC) via hydrothermal carbonization for the removal of methylene blue from aqueous solution. In the study, hydrochar was synthesized at an optimized carbonization temperature (200 °C) with a production yield of 82.75% and a methylene blue removal of 75.93%. The adsorption capacity of adsorbent enhanced with the increasing initial dye concentration due to high driving force for efficient mass transfer. The hydrochar was capable of attaining its maximum adsorption capacity at 131.58 mg/g. The derived hydrochar performed a higher uptake of dye molecules under basic conditions rather than acidic conditions owing to the presence of OH group for the attachment of cationic dye. It was determined that Freundlich isotherm and pseudo second order kinetic models best fitted the experimental data. External film diffusion was found to be the rate-controlling step for the batch adsorption process. The results revealed that MPHTC is a promising adsorbent for treatment of cationic dye for effluent wastewater.

Kinetic Adsorption of Heavy Metal (Copper) On Rubber (Hevea Brasiliensis) Leaf Powder

This research was carried out to study the adsorption of copper from aqueous solution onto rubber leaves powder (RLP) using a batch adsorption process. The functional groups responsible for the adsorption of copper onto the rubber leaves surface were investigated using the Fourier Transform Infra-red (FTIR). Factors influencing adsorption, for example, contact time, adsorbent dosage, pH, copper concentration, particle size, and temperature were also studied. The maximum Cu (II) ions adsorption was observed to have occurred at a pH of 5. The adsorption capacity of Cu (II) ions reduced as the particle size and adsorbent dose increased. The Kinetic studies showed a good correlation and best matched the kinetic model of a pseudo-second order. The Freundlich and Langmuir isotherm models were used to describe the Cu (II) adsorption onto the rubber leaves powder. The data gotten from the adsorption process were best compliant with the Langmuir model with a correlation value of 0.9912 and a maximum adsorption capacity of 9.074 mg / g. The thermodynamic variables (parameters) like entropy change (∆S°), Gibbs-free energy change (∆G°) and enthalpy change (∆H°) were determined and the adsorption process was observed to be an exothermic and a spontaneous process. The adsorption of copper ions from aqueous solution using rubber leaves power involved physisorption mechanism.

Purification of vitamin E from palm fatty acid distillate through neutralization, extraction, and adsorption methods

Vitamin E is one of the compounds in palm fatty acid distillate (PFAD) which was carried away due to thermal treatment in the deodorization unit in the refining of crude palm oil (CPO). The process of purifying vitamin E can be done by combining several common processes such as neutralization, extraction, and adsorption. The neutralization process is carried out to remove the content of free fatty acids (FFA), which are the saponifiable compounds and the largest component in PFAD. FFA in PFAD were first neutralized using magnesium oxide and most of FFA removed during process. Vitamin E and the remaining FFA are carried away during the extraction process with hexane due to similar polarity. Vitamin E extracted from neutralized PFAD was then subjected to batch adsorption process using incubator shaker with silica as the adsorbent. The adsorption process in this study resulted in a vitamin E uptake percentage of 98%. Isopropanol is used as solvent in the desorption process and produces a vitamin E recovery percentage of 96,9%. The concentration of final concentrate was obtained with vitamin E purity of 5,6% (12282 ppm) and the amount increased 9.2 times compared to concentrate from neutralization followed by extraction process. The concentrate has strong antioxidant activity as evidenced by the IC50 value of 23,3 ppm.

Treatment of wastewater from a dairy plant by adsorption using synthesized copper oxide nanoparticles: kinetics and isotherms modeling optimization

Dairy plants produce 1 to 4 L of wastewater per 1 L of processed milk. The wastewater contains high values of chemical oxygen demand (COD) and biochemical oxygen demand (BOD) concentrations, in addition to high levels of dissolved solids. In this study, synthesized copper oxide nanoparticles (CuONPs) coupled with Sophora Japonica fruit, were used as an adsorbent, for the first time, to treat the effluent of dairy plants in a batch adsorption process. The analysis techniques, Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscopy (SEM) were utilized to characterize the adsorbent. The COD removal, using (CuONPs)-based adsorbent, was investigated by varying contact time, masses of the adsorbent, initial COD value and temperatures. The optimum conditions for highest removal percentage were contact time of 120 min, a temperature of 25 °C, pH value of 7.5, and 1 g of adsorbent. The initial COD values used were in the range of 100-700 ppm. The COD percent removal was in the range of 77 to 95%. Freundlich isotherm exhibited the best fitting for the results (R2 = 0.998) with a favorable spontaneous exothermic adsorption process. Based on the calculated normalized deviation value, the modified diffusion model, intra-diffusion, and pseudo-second-order kinetics all showed very good fitting for the adsorption data as indicated by the kinetics study.

Synthesis and Characterization of Electrospun Carbon Quantum Dots – Polyacrylonitrile/Polycaprolactone Composite Nanofiber Membranes for Copper (II) Adsorption

Heavy metal adsorption (HMA) is one of the remediation techniques used to remove heavy metals from water/wastewater. Composite membranes with functionalized additives for selective adsorption are being investigated. In this study, Carbon Quantum Dots – Polyacrylonitrile/Polycaprolactone nanocomposite membranes are synthesized by electrospinning which is intended for HMA of Cu2+. The nanofiber mats were characterized using SEM, FTIR, and Contact Angle. Batch adsorption process were performed and to utilize the AAS for kinetic adsorption behavior analysis. SEM micrographs revealed the addition of CQD in PAN and PAN/PCL membrane matrix shifted the fiber size distribution from 50 – 100 nm to 150 – 250 nm indicates the decrease in effective surface area. FTIR analysis exhibited vibrational peaks and binding of distinct functional groups such as amine, nitrile, carboxylic, hydroxyl, and carbonyl for CQD, PAN and PCL, respectively. CQD in aqueous form further increases the hydrophilicity of PAN/PCL membrane matrix which is essential for HMA of Cu2+ions. The increase of nanofiber mat’s adsorption capacity with respect to contact time obtained a maximum at 63.45 mg/g with a maximum efficiency of adsorption at 90.74%. Kinetic adsorption studies show that the pseudo – first order kinetic model best fits the data for CQD – PAN/PCL nanofiber mat in Cu2+ions obtaining a correlation value of R2= 0.9418 and a rate constant k = 0.0172 min1indicating the adsorption behavior follows the physical adsorption process involving Van der Waals forces and hydrogen bonding between the adsorbent and adsorbate.

Methylene Violet Dye Adsorption Using Onion Skins: Kinetics and Isotherm Studies

This study examined the use of Onion Skins, an inexpensive adsorbent material, for removing the Methyl Violet dye which represents the main objective by using batch adsorption process to investigate and understand the adsorption behaviour, the kinetics and the equilibrium isotherm using a low-cost adsorbent. The study included the influence of contact time and the dosage of adsorbent experiment. The Onion skins was dried, cleaned and crushed. Batch experiments were applied to study the contact time effect using dye with an initial fifty milligram per litter concentration, and different amounts (0.5, 1.0, 1.5, 2.0) gm of adsorbent were used to study the dosage effect. The batch experiment showed a good dye removal with 51.3% during the first 150 min and 54.03% using 1.0 gm of adsorbent. Three kinetics models were applied: Pseudofirst, pseudosecond order and adsorption model for intraparticle diffusion. Pseudosecond and intraparticle diffusion were highly fitted models with a correlation of 0.9998 and 0.9691 respectively. Isotherm study was applied using the Langmuir, Freundlich and BET model, Freundlich model was best fitted model with a correlation of 0.9945, which suggesting a multilayer adsorption.

Kinetics of adsorption of methylene blue onto activated kolanut pod

A batch adsorption process was carried out by optimizing, the effect of contact time (10min to 180min) and initial concentration (5mg/l to150mg/l). The adsorbent was characterized using FTIR spectra and SEM, and the result obtained showed shifting and disappearance of peaks after adsorption. The results of the adsorption kinetics, which includes the correlation coefficient 0.9771 and the agreement between the amount adsorbed experimentally (1.472mg/g) and the calculated amount absorbed(1.196mg/g) revealed that MB was adsorbed satisfactory according to the pseudo second-order kinetic model.

Development of adsorbent from Mentha plant ash and its application in fluoride adsorption from aqueous solution: a mechanism, isotherm, thermodynamic, and kinetics studies

In the present study, Mentha plant ash was modified by Na and Al for the synthesis of adsorbent and applied for the removal of Fluoride from an aqueous solution. Mixture of acid washed Mentha plant ash (MPA) and NaOH (in the ratio 1:1.3) thermally treated at 600°C in a muffle furnace then treated with aqueous solution of sodium aluminate. The characterization of sodium aluminum modified ash (Na-Al-MA) powder was done such as SEM (Scanning Electron Microscopy), Particle Size Analysis (PSA), Fourier transformed spectroscopy (FTIR), Zeta Potential, XRD (X-ray Diffraction) analysis, and Brunauer–Emmett–Teller (BET) analysis. The removal of fluoride from an aqueous solution carried out with Na-Al-MA by batch adsorption process. The Na-Al-MA was found to be very effective as adsorbent. The maximum removal of fluoride was achieved ̴ 86% at neutral pH and at room temperature. It was investigated that Langmuir adsorption isotherm and pseudo-second-order kinetic was best fitted for fluoride adsorption. The fluoride adsorption on Na-Al-MA was an exothermic process. A possible mechanism including electrostatic attraction, hydrogen bonding, and metal-fluoride interaction for fluoride adsorption on Na-Al-MA have described in this study. Novelty statement: Utilization of Mentha plant ash for the development of adsorbent and its application in adsorptive removal of fluoride from aqueous solution is the novelty of this work. Adsorbent preparation may be the better way of waste biomass management.

Highly effective adsorption of antibiotics from water by hierarchically porous carbon: Effect of nanoporous geometry.

Pharmaceutical antibiotics have recently become emerging environmental contaminants. To enhance the removal efficiency of antibiotics in water, hierarchically porous carbons (HPCs) with designed porous patterns are used in both batch and column mode adsorption processes in this study, and the role of their nanoporous geometry in the adsorption dynamics are explored. THPC (HPC with trimodal pores) and DHPC (HPC with bimodal pores) exhibit remarkably superior adsorption performances to the selected antibiotics than those of commercial activated carbon (AC) with similar surface area, especially in column mode adsorption. The effective treatment volumes of the HPC-columns remain up to 8-10 times those of the AC-columns for the removal of tetracycline and 4-6 times for the removal of tylosin. The mass transfer rates of the carbon-based columns present the order of THPC>DHPC>AC. As comparison, the columns based on monomodal mesoporous carbon (MEC) and microporous carbon (MAC) exhibit low effective treatment volumes although their high mass transfer speed. The interconnected meso/macropores in HPCs benefit the intraparticle mass transfer of guest molecules and the accessibility of adsorption sites. The micropores linking to the meso/macropores not only provide adsorption sites but also facilitate adsorption affinity.

Reusing menengic (Pistacia terebinthus) coffee waste as an adsorbent for dye removal from aqueous solution

ABSTRACT The aim of this study is to characterise a bio-waste natural material and investigate its reuse for other purposes. Menengic (Pistacia terebinthus) coffee bio-waste (MCW) was characterised and used to remove malachite green oxalate (MGO) and methylene blue (MB) from aqueous solutions. Characterisation of adsorbent was performed with Brunauer-Emmett-Teller method, Fourier-transform infrared spectroscopy, scanning electron microscopy, and X-ray diffraction techniques. Adsorption parameters such as pH, amount of adsorbent, contact time, mixing speed, initial dye concentration, and temperature were investigated by classical batch adsorption process. Maximum dye adsorption (99.59 ± 0.05% for MGO and 96.54 ± 0.21% for MB) onto MCW were observed at pH values of 8 and 6, and 150 mg and 200 mg of adsorbent in 200 mg/L dye solution at 25°C for 45 min with a mixing speed of 400 rpm, respectively. In this context, Langmuir, Freundlich and Temkin isotherms were tested and it was found that the most suitable isotherm for the experimental data was the Langmuir isotherm with an R2 value of 0.9915 for MB and 0.9852 for MGO. In addition, the maximum adsorption capacity for MGO and MB was determined as 59.17 mg/g and 32.68 mg/g, respectively. The adsorption characteristics of MGO and MB indicate that they coincided with pseudo-second-order kinetics. According to this kinetic model, the mechanism is compatible with chemisorption as the rate determination step and the thermodynamic data suggested the spontaneous and exothermic process.

Efficient removal of pharmaceuticals from water using graphene nanoplatelets as adsorbent.

Recently, pharmaceutical pollutants in water have emerged as a global concern as they give threat to human health and the environment. In this study, graphene nanoplatelets (GNPs) were used to efficiently remove antibiotics sulfamethoxazole (SMX) and analgesic acetaminophen (ACM) as pharmaceutical pollutants from water by an adsorption process. GNPs; C750, C300, M15 and M5 were characterized by high-resolution transmission electron microscopy, Raman spectroscopy, X-ray diffraction and Brunauer–Emmett–Teller. The effects of several parameters viz. solution pH, adsorbent amount, initial concentration and contact time were studied. The parameters were optimized by a batch adsorption process and the maximum removal efficiency for both pharmaceuticals was 99%. The adsorption kinetics and isotherms models were employed, and the experimental data were best analysed with pseudo-second kinetic and Langmuir isotherm with maximum adsorption capacity (Qm) of 210.08 mg g−1 for SMX and 56.21 mg g−1 for ACM. A regeneration study was applied using different eluents; 5% ethanol-deionized water 0.005 M NaOH and HCl. GNP C300 was able to remove most of both pollutants from environmental water samples. Molecular docking was used to simulate the adsorption mechanism of GNP C300 towards SMX and ACM with a free binding energy of −7.54 kcal mol−1 and −5.29 kcal mol−1, respectively, which revealed adsorption occurred spontaneously.

Simultaneous Determination and Optimization of Titan Yellow and Reactive Blue 4 Dyes Removal Using Chitosan@hydroxyapatite Nanocomposites

Chitosan (CS) and hydroxyapatite (HA) nanocomposites have been prepared and used for the simultaneous removal of Titan Yellow (TY) and Reactive Blue 4 (RB 4) dyes from aqueous solutions in single and binary batch systems. Chitosan@hydroxyapatite nanocomposites (NCs) were characterized by diverse techniques such as EDX, FTIR, TGA, and FESEM. Derivative spectrophotometry (DS) was developed to the determination of TY and RB 4 in two-compound mixtures employing the ‘zero-crossing’ technique. The influence of operational variables (such as sorbent mass, contact time, pH, and initial concentration of dyes) on the dyes adsorption is evaluated. A response surface methodology based on a Hybrid central composite design is used to optimize the removal of dyes by CS@HA NCs through a batch adsorption process. In optimum conditions (pH = 4, sorbent dosage = 0.03 g TY (initial TY concentration) = 1100 mg L−1 and RB 4 (initial RB 4 concentration) = 950 mg L−1), the maximum uptake capacities of dyes were obtained 170.7 and 118.4 mg g−1 for TY and RB 4 dyes, respectively. The Langmuir isotherm model was convenient for elucidating the dye adsorption process in both single and binary solutions. The adsorption kinetics of both TY and RB 4 dyes were in best correlation with pseudo 2nd order model. The thermodynamic calculations elaborated that the adsorption of TY and RB 4 dyes was endothermic and spontaneous.

Optimization of the adsorption of total organic carbon from produced water using functionalized multi-walled carbon nanotubes

This study investigated the removal of Total Organic Carbon (TOC) from produced water by batch adsorption process using adsorbents developed from Multi-Walled Carbon Nanotubes (MWCNTs). The MWCNTs, synthesized by catalytic chemical vapour deposition method using kaolin-supported tri-metallic (iron-cobalt-nickel) catalyst were purified by H2SO4/HNO3 and then functionalized with 1-pyrenebutanoic acid N-hydroxyl succinimidyl ester (PSE). The raw, purified and functionalized MWCNTs were characterized by High Resolution Scanning Electron Microscopy (HRSEM), High Resolution Transmission Electron Microscopy (HRTEM), Brunauer–Emmett-Teller (BET) and Fourier Transform Infrared Spectroscopy (FTIR). In the results, HRSEM/HRTEM revealed the structure, purity and also confirmed the attachment of the PSE molecule onto the nano-adsorbent(s). The BET surface areas of MWCNTs, PMWCNTs and FMWCNTs were 970.17, 869.25 and 831.80 m2/g, respectively while the FTIR established the existence of surface functional groups. The functionalized MWCNTs (FMWCNTs) nano-adsorbent showed superior performance efficiency (93.6%) than the purified MWCNTs (PMWCNTs) (79.2%) as examined under the same batch adsorption condition: 0.02 g adsorbent dosage, 10–90 min contact time and 30 °C solution temperature probably, due the improved wettability resulted from incorporation of PSE. Subsequently, Central Composite Design (CCD) was applied to optimize the process parameters for the sorption of TOC onto FMWCNTs. The CCD in the response surface methodology predicted 260 mg/g adsorption capacity of FMWCNTs in the removal of TOC at the optimum condition of 49.70 min contact time, 34.81 °C solution temperature, and 0.02 g adsorbent dosage. The kinetics data were best described by pseudo-second-order model and thermodynamic parameters suggested that the process was feasible, spontaneous and exothermic. It can be inferred from the various analysis conducted that the developed FMWCNTs nano-adsorbent is effective for removal of TOC from oil-produced water and may be explored for removal of organic contaminants from other industrial wastewater.

Adsorption of Cd(II) ions from aqueous solution using fruits peel as cost effective adsorbents

The adsorption of cadmium ion onto different fruits peel i.e lemon, orange and banana has been investigated by batch adsorption process with the variation in the pH, metal ion concentration, adsorbent dose and contact time. The results showed maximum removal efficiency of 94.7%, 98.4%, and 83.6% for banana, lemon and orange respectively. Freundlich and Langmuir adsorption isotherm models have been applied. Langmuir adsorption isotherm model is best fitted in the adsorption showing monolayer adsorption of Cd(II) ion. Pseudo first order and second order kinetics were applied showing higher r2 values for second order kinetics. Pseudo-first order rate constant (k1) for lemon, banana and orange are 0.1384, 0.1387, and 0.1451 whereas Pseudo-second order rate constant (k2) for lemon, banana and orange are 0.857, 0.808 and 0.738 respectively.

Experimental studies on the removal of heavy metal ion concentration using sugarcane bagasse in batch adsorption process

Experimental studies on the removal of heavy metal ion concentration using sugarcane bagasse in batch adsorption process

ADSORPTIVE CAPACITY OF COFFEE HUSK IN THE REMOVAL OF CHROMIUM (VI) AND ZINK (II) FROM TANNERY EFFLUENT: KINETICS AND EQUILIBRIUM STUDIES

Tannery wastewater is the most challenging due to the complex toxic pollutants it releases into the environment. Similarly, coffee husk from coffee processing operations pollutes the environment. The use of coffee husk to remove hexavalent chromium (VI) and Zink (II)from tannery wastewater solves pollution problems due to untreated tannery wastewater and coffee husk. A batch adsorption process was conducted to determine chromium (VI) and Zink (II)adsorptive capacity of waste coffee husk to treat tannery wastewater. The effects of adsorbent dose (0.2-2.4 g/L), contact time (20- 60 min), agitation speed (50-250 rpm), and pH value (2-8) on the adsorptive capacity of coffee husk on the removal of hexavalent chromium (VI) & zinc (II) from tannery wastewater were studied. Using 2.4 g/L adsorbent dose, 250 rpm agitation speed, 60 min contact time, and pH value of 2, a maximum Cr(VI) removal capacity of coffee husk was 83%. The maximum Zn(II) removal capacity of coffee husk was found to be 79% at an adsorbent dose of 2.4 g/L, 60 min contact time, pH 7, and agitation speed of 250 rpm. Therefore, it can be concluded that coffee husk achieved significant removal of hexavalent chromium (VI) and zinc (II) from tannery wastewater.

ADSORPTION STUDIES OF FULLERS EARTH NANOCOMPOSITES FOR THE REMOVAL OF COPPER AND REACTIVE YELLOW 18

Fuller's earth of D. G. Khan was used as a low-cost adsorbent to remove copper and reactive yellow 18 from aqueous solutions as it has the capacity of adsorption of toxic particles in its structure. Because of this capacity to take up the ionic component, utilization of fuller's earth has experimented for the purification of wastewater in the laboratory. Sampling and physical processing by grinding and sieving/classification were conducted. Characterization of fuller's earth (adsorbent) was carried out by X-Ray Fluorescence (XRF), Scanning Electron Microscope (SEM), and Fourier Transform Infrared (FTIR). The result of XRF revealed the presence of large proportion of metal oxides like TiO2 (0.78%), Fe2O3 (3.13%), Al2O3 (12.38%), MgO (2.16%), CaO (10.73%), Na2O (0.22%), P2O5 (0.11%), Cl (0.03%), K2O (2.63%), MnO (0.03%), C (1.30%) and SiO2 (66.31%) in the fullers earth. SEM images show the morphology, porous nature, and different micro size particles of the adsorbent. FTIR results show the presence of different functional groups. The batch adsorption process was performed, and different operating parameters such as contact time, the concentration of fuller's earth, adsorbate concentration, pH values, and temperature were evaluated to find the maximum level of adsorption. Contact time of 100 minutes, 100 mg/L initial adsorbate concentration, 0.5 g adsorbent dosage at 65 oC temperature are the optimum values at which percentage removal is maximum, i.e., 96% for copper at pH 6 and 68% for reactive yellow 18 at pH two by Fullers earth was achieved. The solid addition method describes the pH point of zero charges, which is 4 for fuller's earth. Maximum adsorption at high temperature indicates that this adsorption process is endothermic.