Article Publishing History Article Received on : 24 May 22 Article Accepted on : 20 Jun 22 Article Published : 10 Aug 2022 Plagiarism Check: Yes Reviewed by: Dr. Chuah Lee Siang Second Review by: Dr. Adhidesh Kumawat Final Approval by: Dr. Carmiña Gartner Vargas
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ABSTRACT:
The binary and ternary adsorptions of Pb (II), methyl orange (MO) and brilliant blue (BB) on engineered biochar (Fe2O3-BC) nano-composite using pyrolysis and microwave activation were investigated in this work. Batch experiments were conducted to investigate the capacity of Fe2O3-BC to remove MO, Pb and BB in binary and ternary aqueous solutions. MO removal was higher in MO-Pb binary solution than in ternary MO solution. A large amount of adsorbent dosage, high concentration and longer time were witnessed to achieve maximum removals in ternary solutions as compared to binary solutions. The Langmuir plots indicated that the isotherm can be used to describe sorption studies of both MO dye and Pb2+, while Temkin isotherm was not in agreement with the results. The closeness of R2 value to 1 indicated that the data obtained fits Langmuir Isotherm model of monolayer adsorption kinetics. It was concluded that the Fe2O3-BC nano-composite has a series of distinct homogeneous sites available for binding the MO anions in solution. Therefore, the use of Fe2O3-BC nano-composite for small scale community water purification is a novel cause.
KEYWORDS:
adsorption; adsorbate; Biochar; biosorption; heavy metal; pyrolysis
Copy the following to cite this article:
Shumba. T. T, Musamirapamwe B. V. Investigation on the Adsorption Properties of an Engineered Biochar (Fe2O3-BC) Nano-Composite in Binary and Ternary Aqueous Solutions. Mat. Sci. Res. India;19(2).
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Shumba. T. T, Musamirapamwe B. V. Investigation on the Adsorption Properties of an Engineered Biochar (Fe2O3-BC) Nano-Composite in Binary and Ternary Aqueous Solutions. Mat. Sci. Res. India;19(2). Available from: https://bit.ly/3dgXxR6
Introduction
Wastewater, if managed well, can be an important water resource especially in maintaining environmental flows and groundwater recharge in dry seasons. In Harare, the water supply dams are situated downstream of the city in order to increase the catchment yields. However, this has brought to the fore the issue of pollution from untreated wastewater streams from both domestic and industrial sources. To reduce the amount of pollutants flowing into Lake Chivero, the Harare City Council used to use treated sewage effluent to irrigate pasture in 1970. This method of pollution reduction was effective to an extent that in the late 1970s it was observed that the pollution returned to minimum levels16. However, the increase in the volume of wastewater generated over the years and the availability of arable land close to the wastewater treatment plants have reduced the impact of pasture irrigation on lowering the pollution levels in Lake Chivero.
Wastewaters are produced in many industrial processes, mostly from mining, steel mills, tanning plants, production of chemical fertilizers and pesticides, fabric dyeing plants, electroplating plants, motor and power engineering plants, and battery and accumulator production plants3,4.6,7,8,12,13. These industries and others can be found within the Lake Chivero catchment area. Untreated waste streams eventually find their way into the lake. Heavy metals have always been a part of our ecosystem; however, their relative concentrations have increased due to civilization and industrial development. In aquatic environments, heavy metals show high mobility. Plant roots take up heavy metals which may end up in the digestive systems of humans and animals. Heavy metals pose serious threats to living organisms due to toxic effects on certain elements of the environment and bioaccumulation in the food chain9,10,11. The methods commonly used for metal ions removal from aqueous streams are chemical precipitation, lime coagulation, ion exchange, reverse osmosis and solvent extraction48. New technologies for removal of toxic metals from wastewaters have focussed attention on biosorption because biological materials have strong metal binding capacities15,16,18.
Dye adsorption studies done in the presence of a heavy metal give more insight on the removal capabilities of biosorbents. This is so because adsorption technologies are one of the most effective methods for dye removal due to their high efficiency, low cost, and ease of operation56. Dye removal from aqueous solutions will provide a medium of study for this current investigation. However, it is important to note that wastewaters contain various heavy metals in solution. It is prudent to carry out experimental work where one or more heavy metal is under study17,18,20,21.
Biochar (BC) is prepared by pyrolysis (300°C and above) of a biomaterial in the absence of air until all the organic compounds except carbon are volatilised47. It has been used for tertiary treatment of municipal and industrial wastewaters23. Biochar adsorbs soluble organics namely nitrogen, and sulphides, in wastewater following biological or physical–chemical treatment23. Biochar though effective in adsorption, is limited to waste streams with low organic concentrations (less than 5%), low inorganic concentrations (less than 1%) and unable to remove highly soluble organics, or those with low molecular weights22. To counter BC deficiencies in adsorption, there is need to activate it and enhance it with an oxide. Iron oxide has been used as an adsorbent in several studies in aqueous solutions36, however, to increase the number of adsorption sites, impregnated BC is among the adsorbents available for such studies.
The synthesis of activated biochar using microwaves is an area that needs more investigation because biochar generation from paper and pulp sludge has not received much research attention to date. Chaukura14 reported an increase in surface area and porosity on microwave generated biochar, which was accompanied by an increase in the adsorption capacity of the adsorbent. In addition, the smaller the particle size the greater the surface area for adsorption, so the activated BC ground to nano scale is expected to adsorb more. An activated metal oxide biochar nano-composite represents an emerging group of adsorbents for removal of neutral and ionic contaminants in aqueous solutions22-32.
There are very few researches on binary33,34,38,50,52,55,57 and ternary1,37,52,54 adsorption studies on aqueous solutions. Shaaker63 researched on ternary dye adsorption onto manganese oxide (MnO2) nanoparticles loaded with activated carbon and concluded that MnO2-NP-AC had a high adsorption capacity when compared to other adsorbents for dye removal from an aqueous medium. Mckay26 noted that traditional models for multicomponent isotherms improperly fit the аdsorption dаta of systems with both synergistic and antаgonistic adsorption and needed RSM models to fit for data correlation. In a multicomponent study by Walker and co-workers42, activated carbon showed high adsorption capacity for dyes in single phase systems and equilibrium adsorption capacities decreased in multicomponent systems as compared to single dye systems as the solution matrix become complex35,39,40,41. The experimental data was described by Langmuir Isotherm model which might indicate that the number of adsorption sites available for dyes on activated carbon is limited; hence the idea of impregnating BC with iron oxide could increase the number of active sites for adsorption58-62.
This current study focused on lead (Pb), methyl orange (MO), brilliant blue (BB) removal in aqueous solutions. Experimental applications were done in binary and ternary solutions using engineered metal oxide biochar nano-composite. Effects of pH, contact time and concentration were investigated.
Materials and Methods
Chemicals and Materials
The following chemicals and materials were used in this study: paper and Pulp Sludge (PPS), potassium hydroxide (KOH) analytical grade, hydrochloric acid (HCl), iron chloride (FeCl3), deionised water, pH meter (Mettler Toledo), Shaker (Merck) and microwave (Samsung).
Preparation of Fe2O3-BC
The Fe2O3-BC was prepared using the following procedure5,14. A 500 g of Paper and Pulp Sludge (PPS) obtained from Kadoma Paper Mills, dried at 105 °C for 24 hours was pre-ashed to remove volatiles in an oven at 200 °C for 2 hours in an air tight container. The carbonization of the pre-ashed PPS was carried out in a muffle furnace at 500°C and 700°C separately for 2 hours. Potassium hydroxide (KOH, 5 grams) was used to impregnate the biochar (1:2). Deionised water (100 ml) was added to dissolve all the KOH pellets, and the mixture left for 24 hours at room temperature. Further activation of the impregnated BC was carried out using a microwave (800 watts) for 6 minutes. The sample was then cooled at room temperature and washed with hot distilled water. In preparation of Fe2O3-BC, 12 grams of BC were thoroughly mixed with 4 grams of FeCl3 solution. The mixture was put in a muffle furnace at 700°C for 2 hours. The Fe2O3-BC samples were ground, sieved through 250 µm and stored in a closed container for use.
The percentage conversion of PPS to BC was calculated as:
Where m1 is the starting mass of PPS and m2 is the mass of BC produced. The percentage conversion was 24% at 700°C.
Characterisation of Biochar and Fe2O3-BC
The Fe2O3-BC sample wascharacterised using Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM) for surface area analysis.
Fourier-Transform Infrared Spectroscopy (FTIR)
Infrared spectroscopy (FTIR 3000, WQF-520, attenuated) was used to identify the functional groups present in the synthesized samples of biochar before and after adsorption. The FT-IR studies were carried out in the 4000 to 400 cm-1 wavenumber range. Background correction was done first and the dried solids were pressed with FTIR grade KBr and the pellets scanned 32 times using transmission mode with a resolution of 4 cm-1.
Adsorption Studies
The adsorption properties of the synthesised Fe2O3-BC were determined by application in known heavy metal and dye concentrations in aqueous waste water. The UV/VIS Spectrophotometer (Lasany Double Beam LI-2802) and FAAS (AA-6701F) were used for Lead and Methyl Orange concentrations measurements. Three replicates of different concentrations were prepared one for lead removal and the other for methyl orange removal. The analysis limits were 0.1 µg/L for Pb. Stock solutions 1000 ppm each of Lead and Methyl orange were prepared in 1 litre distilled water. And afterwards, solutions were diluted to different concentrations. The pH values of solutions were adjusted by addition of HCl and sodium hydroxide (NaOH).
Effect of time
In MO binary solutions, the effect of shaking time was studied by shaking 50 mg of Fe2O3-BC for 15, 30, 60, and 90 minutes in a 20 ml of 50 mg/L of MO solutions spiked with 5 mg/L Pb. Binary solutions of Pb experimental time effect was determined by shaking 50 mg of Fe2O3-BC for 15, 30, 60, and 90 minutes in a 50 ml of 5 mg/L of Pb solutions spiked with 50 mg/L MO. In ternary solutions experiments, the effect of contact time was studied by shaking 50 mg of Fe2O3-BC for 15, 30, 60, and 90 minutes in a 20 ml of 50 mg/L of MO solutions containing 5 ppm Pb and 50 mg/L BB. For Pb, the effect of contact time or shaking time was studied by shaking 50 mg of Fe2O3-BC for 15, 30, 60, and 90 minutes in a 50 ml of 5 mg/L of Pb solutions containing 5 mg/L Pb and 50 mg/L BB.
Effect of pH
The effects of initial pH on adsorption for Pb were investigated at pH 2, 4, 10 and 12 using a 50 ml solution of 5 mg/L for Pb, with 50 mg of Fe2O3-BC. For MO dye the effect of initial pH on adsorption were investigated at pH 2, 4, 8, 10 and 12 using a 20 mL of 50 mg/L of MO solutions of 50 mg Fe2O3-BC.
Effect of concentration
In the binary and ternary solutions, the effect of initial dye concentration was studied using five initial concentrations (50, 100, 150, 200 and 250 ppm) for each 50 mg adsorbent (Fe2O3-BC) in a 20 ml solution spiked with 5 ppm Pb and 50 mg/L BB. The effect of Pb and BB concentrations were carried out by varying their concentrations (50, 100, 150, 200 and 250 mg/L separately for BB and 5, 10, 15, 20 and 25 ppm for Pb separately) in a 20 ml of 50 mg/L MO solutions for 30 minutes.
Effect of dosage
For binary solutions, the effect of adsorbent dosage (50, 100, 150, 200, and 250mg of Fe2O3-BC) was performed by shaking a 20 ml solutions of MO containing 5 mg/L Pb for 30 minutes. For Pb, the effect of adsorbent dosage (50, 100, 150, 200 mg, Fe2O3-BC) were done by shaking a 50 ml solution of 5 ppm of Pb containing 50 mg/L MO for 30 minutes. In ternary solutions, the effect of adsorbent dosage (50, 100, 150, 200, and 250 mg of Fe2O3-BC) were performed by shaking a 20 ml solutions of MO containing 5 mg/L Pb and 50 ppm BB for 30 minutes. For Pb, the effect of adsorbent dosage (50, 100, 150, 200 mg, Fe2O3-BC) were done by shaking a 50 ml solution of 5 mg/L of Pb containing 50 mg/L MO and 50 mg/L BB for 30 minutes.
The initial and equilibrium concentrations of Pb2+ ions and MO in solutions were measured to calculate the amount adsorbed using the equations:
Equation 3 was used to calculate percentage removal. Where Ci and Ce are the initial and equilibrium concentrations of Pb2+ ions and MO in ppm, Qe is the amount of Pb2+ ions and MO adsorbed at equilibrium in mg/g, V is the volume of Pb2+ and MO solutions (L) and m is the mass of Fe2O3-BC in grams (Nharingo et al., 2013, Alatalo et al., 2013, Coimbra et al., 2015, Chaukura et al., 2016, Petrovic et al., 2016)
The Langmuir and Temkin equations were used to describe the equilibrium between the adsorbate and adsorbent represented as:
Where Qmax, and kl are the maximum adsorption capacity for the solid phase loading and the energy constant related to the heat of adsorption respectively. Plotting Ce/Qe versus Ce, gives a straight line with Qmax and kl determined from the intercept and the slope of the graph respectively. Also a plot of Qe versus lnCe gives a straight line (Li et al., 2012, Nechifor et al., 2015)
Results
The experimental results are presented in this chapter.
Iron Oxide FTIR Spectra
Figure 1: Fe2O3-BC FTIR Scan (a) after adsorption and (b) before adsorption.
There were no major changes in percentage removals on increasing the concentration of BB, major changes were observed on altering the dosage and the concentration of Pb.
This chapter consists of analysis and discussion of results in detail.
Characterisation
Figure 1 shows –OH stretching as can be depicted from the peaks in the range of 3300-3500 cm-1. Also present were hydroxyl groups, 2925 cm-1 -CHx stretching bands, 1600 cm-1 related to the aromatic structure, 1390 cm-1 phenolics -OH, 830 cm-1 alkene CH band, 600 cm-1 due Fe-O bond and 490 cm-1 regions with Fe2O3-BC. The 490 cm-1 region with Fe2O3-BC show the presence of Iron oxide. This is in agreement with literature (Chaukura et al., 2016). The major differences between the peaks before adsorption and after adsorptions were where the 1100 cm-1 peak broadened to stretch from 9750- 1275 cm-1 corresponding to the MO fingerprint region (Gomez et al., 2014). This indicates the effect of heavy metal and dye addition. Figure 2 shows the Methyl Orange Spectra with unique finger print region between1500 – 0 cm-1. On the after adsorption scans, the regions 9750- 1275 cm-1 is mainly incorporated in the adsorbents. For figure 3 the SED was 10kV and 5kV respectively. It affected the clarity of the image. After adsorption both biochars had reduced surface area.
Effect of pH
Figure 4 show that Fe2O3-BC had a highest percentage MO removal of 89.81% at pH 2, beyond pH 8; there is constant percentage removal. This may prove that at pH 2; Fe3+ is more effective in acidic conditions for the removal of MO. Fe3+ ions with the combination of H+ ions present at low pH provided the much needed cationic binding sites for anion MO
Effect of time
Figure 10 shows that the percentage Pb removal increases rapidly to 73% in the first 20 minutes and gradually increase to 79% in a binary Pb aqueous solution. In Figure 7, the percentage Pb removal was rapid in the first 20 minutes to 81%, approached constant from 30 minutes (63%) to 62% after 90 minutes of shaking in a ternary aqueous solution. Fe3+ ions being smaller could have occupied the smaller octahedral voids in the BC, and all the tetrahedral voids left unoccupied. Pb2+ ions due to the size could have been occupying the all the available tetrahedral sites in the BC making the percentage removal differences small. For the binary and ternary solutions, percentage removals decreased from a highest of 97% in the first 20 minutes to a lower value of 73% then increased to 79%. A constant percentage removal of 62% was achieved in ternary aqueous solutions after 90 minutes.
Effect of dosage
In figure 9, after addition of 65 mg of Fe2O3-BC the percentage Pb removal was 85% in binary Pb solution. 150 mg had 69% Pb removal and addition of 250 mg resulted in 76% Pb removal. Figure 13 shows that the optimum dosage of 150 mg Fe2O3-BC in a MO ternary aqueous solution. The percentage removal increased with increased adsorption dosage which can be attributed to the increase of surface area and pores available for the sorption process. On the addition of 200 mg of the adsorbent the percentage removal decreased to 39% which can be explained using desorption studies and increased to 92% after the addition of 250 mg. In figure 18, the percentage removal of Pb in a ternary solution increased rapidly on the addition of 65 mg to 65% compared to 100% in single Pb solutions. This suggests that the addition of impurities (MO and BB) reduced the number of active sites for adsorption to take place.
There were no major changes in percentage removals on increasing the concentration of BB. The effects of addition of Pb and BB were witnessed on the dosage which increased from 100mg to 150 mg (MO ternary solution).
Effect of concentration
Figure 6 shows the percentage removals of Pb in a binary solution where 50 mg/L of MO were with a maximum removal of 95% of Pb. Constant percentage Pb removal (84%) was witnessed between 15 and 25 mg/L of Pb added. The effects of varying MO concentration in a 5 mg/L Pb solution are represented in figure 7 where the maximum removal was at 71% Pb removal after the addition of 100 mg/L MO. There is a deep at 150 mg/L of 64% removal and a constant removal of 68% between 200 mg/L and 250 mg/L. In figure 14, the effect of changing the MO concentration in a ternary solution, where 100% removal was achieved after the addition of 70 mg/L of MO. Constant percentage removal was witnessed between 100 and 250 mg/L of MO. Figure 15 shows the percentage removal of 100% Pb after addition of 6.5 mg/L Pb. 96% constant removal was witnessed between 10 and 25 mg/L Pb. In figure 16 (b), 99% of Pb was removed after addition of 60 mg/L MO in a ternary solution. The percentage removals fluctuated until a constant removal was realised between 200 mg/L and 250 mg/L at 60%. Figure 16 (b) shows that 82% Pb ions removal was achieved after addition of 70 mg/L BB concentration of the ternary system. The removal moved constantly towards 76% point between 100 and 250 mg/L BB concentration.
Pb2+ ions might have provided more adsorption binding sites for MO in solution after being incorporated in the unoccupied voids of the Fe2O3-BC. The overall effect of concentration variations is the lowering of the percentage removals of the targeted dye and heavy metal. This is due to the suppression of the active sites as the concentration is increased. As the concentration is varied from binary to ternary solutions, saturation occurred as the percentage removals remained constant across all the solutions.
Isotherms
Figure 11 shows the langmuir isotherm for the sorption of Pb2+ ions onto the adsorbent in a binary solution with R2 value of 0.655 deviating slightly from unity. The multisites provided by Fe3+ and Pb2+ ions present in the binary solution might be reponsible for the deviations in the langmuir plot. Langmuir isotherm fail when the adsorption surfaces become inhomogenous and this adsorption kinetics of binary systems can be better described using pseudo second order kinetics. In figure 12, the Temkin plot with the R2 value of 0.751 shows that the results obtained do not fit well with this isotherm. Figures 11 and 12 describe isotherms of binary solutions. Figures 19 and 20 describe the Langmuir isotherm for the sorption studies of MO dye and Pb2+ ions onto the adsorbent with R2 values of 0.814 and 0.987 respectively. Pb2+ ions are fitting well as compared to MO dye in ternary solutions. Figures 21 and 22 are Temkin plots of Pb2+ ions and MO dye with values 0.819 and 0.00 respectively, suggesting that the MO dye does not fit into this isotherm in a ternary solution. For the Pb2+ions the Langmuir Isotherm plot had the best fit in ternary solution with R2 value of 0.987 suggesting monolayer adsorption is predominant.
Conclusion
The synthesis of iron oxide biochar (Fe2O3-BC) from paper and pulp sludge (PPS) using microwave pyrolysis was successful at 700°C. The maximum adsorption capacity of Fe2O3-BC was 6.50 mg/g. Concentration variations lowered the percentage removals of the methyl orange and lead. This is due to the suppression of the active sites as the concentration is increased. As the concentration is varied from binary to ternary solutions, saturation occurred as the percentage removals remained constant at lower percentage removals across all the solutions. The inclusion of cations (Fe and Pb) addressed the inefficiencies of BC in adsorption towards anions. Iron oxide provided needed binding sites resulting in highest percentage removals. A combination of Fe2O3-BC and Pb in wastewater solutions enhanced anionic compounds adsorption. There were little effects on cations (Pb) removal in aqueous solutions.
The sorption of Pb2+ ions can be described using the Langmuir Isotherm plot which had the best fit in ternary solutions with R2 value of 0.987 suggesting monolayer adsorption is predominant, while the Temkin plot had R2 of 0.819 suggesting that there is no linearity in the decrease of heat of adsorption. The Fe2O3-BC nano-composite used can be said to have a series of distinct homogeneous sites available for binding the MO anions in solution. Studies of the binary MO/Pb2+ and ternary MO/BB/Pb2+ are not common in literature, which makes this experimental data obtained in this work very important in providing the information that could be used in adsorption processes.
Acknowledgement
All source documents consulted were referred in the manuscript.
Conflict of interest
Authors declare no conflict of interest
Funding Source
Publishing funding will be applied for as soon as possible.
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