Volume 10, Number 2 (January 2023):4191-4198, doi:10.15243/jdmlm.2023.102.4191 ISSN: 2339-076X (p); 2502-2458 (e), www.jdmlm.ub.ac.id
Open Access 4191 Research Article
Equilibrium studies for the removal of manganese (Mn) from aqueous solution using natural zeolite from West Java, Indonesia
Ali Munawar1*, Djoko Mulyanto1, RR Dina Asrifah2
1 Faculty of Agriculture, UPN “Veteran” Yogyakarta, Jl. SWK Jl. Ring Road Utara No.104, Condongcatur, Yogyakarta 55283, Indonesia
2 Faculty of Mineral Engineering, UPN “Veteran” Yogyakarta, Jl. SWK Jl. Ring Road Utara No.104, Condongcatur, Yogyakarta 55283, Indonesia
*corresponding author: ali.munawar@upnyk.ac.id
Abstract Article history:
Received 8 November 2021 Accepted 31 October 2022 Published 1 January 2023
Manganese (Mn) is one of the heavy metals found in industrial wastewater, such as acid mine drainage, which has caused serious environmental problems worldwide. This equilibrium study was carried out to determine the maximum capacity of natural zeolite towards manganese removal from made aqueous solution as affected by zeolite quantity, particle size, activation temperature, and initial pH of the solution. The natural zeolites obtained from Tasikmalaya, West Java, Indonesia, were crushed and filtered into three groups of diameters: <0.5, 1-2, and 2-4 mm. Each group was divided into two sub-groups, one sub-group was heated in a muffle furnace at 250 oC for two hours, and the other sub-group was left at room temperature (25 oC). This experiment consisted of two sections. Section one was physical and chemical characterizations of the natural zeolite, using Scanning Electron Microscopy (SEM), X-Ray Diffraction, and X-Ray Fluorescence techniques. The second section was equilibrium studies using two series of 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, and 5 g of natural zeolites of each sub-groups, then respectively added with 50 mL of a solution containing 50 ppm Mn having pH of 5.5 and 7.0.
All suspensions were shaken for 24 h and filtered. The filtrates were red for total dissolved Mn using Atomic Adsorption Spectrophotometer (AAS).
Freundlich and Langmuir isothermic models were fitted to the collected data to describe the adsorptive behaviour of Mn toward natural zeolites. Data showed that 0.5 g of natural zeolite had removed the remarkably highest Mn from the solution, regardless of the size of the particles, thermal treatment, and initial solution pH. The smallest size of zeolite particle and higher initial solution pH tended to increase the adsorptive capacity of the natural zeolite toward Mn. The Freundlich isothermic model fitted better to Mn adsorption behaviour than the Langmuir model.
Keywords:
isothermic models manganese natural zeolite SEM
XRD XRF
To cite this article: Munawar, A., Mulyanto, D. and Asrifah, R.R.D. 2023. Equilibrium studies for the removal of manganese (Mn) from aqueous solution using natural zeolite from West Java, Indonesia. Journal of Degraded and Mining Lands Management 10(2):4191-4198, doi:10.15243/jdmlm.2023.102.4191.
Introduction
Manganese (Mn) is one of the important metals causing environmental problems worldwide, especially due to wastewater such as mine-impacted water surrounding the mining area, which is usually
called acid mine drainage (AMD). At high concentrations, this metal is highly toxic and non- biodegradable; therefore, it must be removed from polluted streams in order to meet allowable environmental standards (Zendelska et al., 2015). A previous study to remove heavy metals from AMD
Open Access 4192 using dolomite addition showed that all dissolved Al
dan Fe metals could be easily removed from the solution when the pH approached 6, but Mn was consistently high, even above 7 (Munawar et al., 2017). Similar findings were also reported by da Silveira et al. (2009) in South Brazil. They found that Mn2+ removal from an aqueous solution required higher pH (closer to 9.0), while other cations (Al3+ and Fe3+) could be removed at lower pH values (closer to 7.0). Therefore other techniques, such as the adsorption process, provide an attractive opportunity to remove Mn2+ from an aqueous solution (Taffarel and Rubio, 2010). One promising option is using natural zeolite.
Natural zeolite is well known as one of the important non-metallic minerals and multi-use industrial minerals in Indonesia (Kusdarto, 2008;
Kadja and Ilmi, 2019). It has been used for various purposes, including environmental protection and industry. Various types of zeolite have been used as adsorbents, a filter of molecular compounds, cell membranes, ion exchangers, and catalysts (Kusdarto, 2008; Masoudian et al., 2013; Zendelska et al., 2015;
Atikah, 2017; Bakalár and Pavolová, 2018). It is also particularly suitable for removing undesirable heavy metals (Zendelska et al., 2015; Atikah, 2017; Bakalár and Pavolová, 2018; Kadja and Ilmi, 2019). Erdem et al. (2004) described natural zeolite could be used effectively as an adsorbent for removing heavy metals such as Co2+, Cu2+, Zn2+, and Mn2+ from wastewater.
Chiban et al. (2012) studied the adsorption and the removal of heavy metals from drinking water by natural zeolite. Wang and Peng (2010) reviewed the utilization of natural zeolites as a metal adsorbent in water and wastewater treatment. These adsorptive properties have been associated with high negative charge density in the zeolites lattice (Belova, 2019) and a large volume of free spaces in the zeolite structure (Krol, 2020)
The objective of this equilibrium study was to determine the maximum capacity of natural zeolite towards Mn removal from made aqueous solution as affected by the zeolite quantity, particle size, thermal activation, and initial pH of the solution. Experimental data were fitted to mathematical models, namely the Freundlich and Langmuir, to predict the adsorption performance of the natural zeolite.
Materials and Methods Characterization of natural zeolite
In this study, natural zeolite samples from Tasikmalaya, West Java, Indonesia, were used and supplied by ADY WATER CV in Bandung, Indonesia.
The original zeolite materials were ground into three groups of diameter: <0.5 mm, 1-2 mm, and 2-4 mm.
Each group was divided into two sets of samples, one set of samples was thermally treated or activated at 250
oC in a muffle furnace for two hours (TR), and the
other was left untreated (OR). Mineralogical and chemical compositions of the natural zeolites were tested using X-Ray Diffraction (XRD) and X-Ray Fluorescence (XRF), respectively, while the cation exchange capacity (CEC) was determined using 1 N ammonium acetate pH 7 method. The XRD and XRF tests were conducted in the Integrated Research and Testing Laboratory (LPPT), Gadjah Mada University, Yogyakarta, Indonesia, while the CEC determination was carried out in the Laboratory of the Agency for Agricultural Technology Research (BPTP), Board of Research and Development, the Ministry of Agriculture, Yogyakarta, Indonesia.
Equilibrium studies
The heavy metal, Mn, was used as an adsorbate in this research. Synthetic single-component solutions of Mn2+ were prepared by dissolving a weighed mass of the analytical grade salt MnSO4·H2O in 1,000 mL distilled water to obtain a 50 ppm Mn solution. The synthetic Mn solution was used to mimic acid mine drainage in a mine environment. This solution was divided into two sets of solutions. One set of the solution was adjusted to pH 7 using a dilute NaOH solution, while the other set of the solution was left as the original (pH 5.5). Adsorption of Mn ions on zeolite was performed with synthetic single ion solutions of Mn2+ ions with 50 ppm to extract the natural zeolite mass of 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, and 5 g. The zeolite mass was put in plastic tubes and added with 50 mL Mn solution (50 ppm), then shaken for 24 h. At the end of the predetermined time, the suspensions were filtered, and the collected filtrates were red in the Atomic Adsorption Spectrophotometer (AAS) in the Laboratory of the Agency for Agricultural Technolgy Research (BPTP), the Ministry of Agriculture, Yogyakarta, Indonesia. The same procedures were applied for both extractions using both Mn solutions of pH 5.5 and pH 7.0.
To describe the equilibrium status and behaviour of Mn adsorption, the two most common mathematical models, the Freundlich and Langmuir isotherms, were used in this study. The Freundlich isothermic model is usually used to describe the adsorption characteristics of the heterogeneous surface. This empirical equation is:
Qe = KfCe1/n ... (1) where:
Kf = Freundlich isotherm constant (mg g-1) n = adsorption intensity constant
Ce = the concentration of adsorbate in the solution at the equilibrium (mg L-1) Qe = the amount of metal adsorbed per gram
of adsorbent at the equilibrium (mg g-1) If equation 1 is linearized, it becomes:
Log Qe = log Kf +1/n log Ce ... (2) (Dada et al., 2012; Ayawei et al., 2017)
Open Access 4193 In the linear relationship between log Qe and log Ce
curve, the log Kf and 1/n become the intercept and the slope, respectively, so the values of Kf and 1/n can be calculated. The constant Kf is an approximate indicator of adsorption capacity, and 1/n is a function of the strength of adsorption. If n=1, then the partition between solid (zeolite) particles and the solution is independent of the concentration. A value of 1/n<1 indicates normal adsorption, meanwhile, 1/n>1 suggests cooperative adsorption. In the Freundlich isotherm, it is assumed that adsorption occurs on heterogeneous surfaces (Dada et al., 2012; Ayawei et al., 2017).
The Langmuir isotherm quantitatively describes the formation of monolayer adsorbate on the outer surface of the adsorbent, and no further adsorption takes place (Dada et al., 2012; Ayawei et al., 2017).
Therefore, the Langmuir represents the equilibrium distribution of metal ions between the solid and liquid phases. This model assumes uniform energies of adsorption onto the surface and no transmigrations of adsorbate in the plane of the surface. The Langmuir equation can be written in the following form:
Qm = QoKL Ce/(1+ KL Ce) ... (3) This equation (3) can be transformed into its linear form:
1/Qm = 1/Qo + 1/(Qo KLCe) ... (4)
(Dada et al., 2012; Murtihapsari et al., 2012) where:
Ce = the equilibrium concentration of adsorbate (mg L-1)
Qm = the amount of metal adsorbed per gram of the adsorbent at equilibrium (mg g-1) Qo = maximum monolayer coverage capacity
(mg g-1)
KL = Langmuir isotherm constant related to adsorption capacity (L mg-1).
Results and Discussion
Physical and chemical characteristics of natural zeolite
Micrographs of natural zeolite samples obtained from SEM analysis are given in Figure 1. The micrographs clearly show a number of macro-pores in the zeolite structure, well-defined crystals of the mordenite zeolites, rough surfaces and many macropores in the zeolite structure, and well-defined crystals of minerals.
The thermal treatment at 250 oC for two hours in a muffle furnace showed more defined structures of the zeolite particles. Neag et al. (2020) stated that rough surfaces were favourable for the adsorption of metals.
Dewi et al. (2016) reported that natural zeolites have various structures depending on the types of zeolites.
a (1000x) b (5000x)
c (1000x) d (5000x)
Figure 1. SEM micrographs of original natural zeolites (a, b) and thermally-treated natural zeolites at 250 oC for two hours (c, d) at two different magnification levels.
Open Access 4194 Mordenite zeolite types, such as those found in Bayah
and Tasikmalaya, West Java, have platy structures, while the clinoptilolite types, as found in Lampung are
tabular. These findings were supported by the results of the X-Ray diffractometer (XRD) tests, as shown in Figure 2.
Figure 2. Difractogram XRD of the natural zeolites.
Figure 2 indicates that the natural zeolites used in this experiment were not pure, with the dominant fraction being mixed clinoptilolite and mordenite zeolite types, with some impurities such as sodium aluminum silicate. A study conducted in the adjacent areas reported two main zeolite types, namely modernite (32.70%) and clinoptilolite (30.89%), found in the areas (Setiawan et al., 2020). Furthermore, Setiawan et al. (2020) stated that mica, plagioclase, and quartz minerals were impurities associated with the zeolites.
Dewi et al. (2016) reported that some other minerals like heulandite, albite, and cristobalite were common impurities in natural zeolites. The chemical compositions of the natural zeolite are presented in Table 1. Data in Table 1 confirm that the natural zeolite used in this experiment contains some impurities, as shown by XRD test data (Figure 2). In addition, the zeolite contained a significant amount of basic cations, especially potassium (K), calcium (Ca), dan magnesium (Mg). This indicates that the zeolites retained exchangeable cations. The data of determining cation exchange capacities (CECs) were 51.91 and 39.44 cmol(+) kg-1 for the original and thermally treated zeolites, respectively. The decrease in CEC after thermal treatment might indicate that some functional groups in the zeolite structure had been damaged. According to Dewi et al. (2016), the exchangeable cations are loosely held near the seat charge within the zeolite structure and can be replaced by other cations in the solution. Furthermore, these authors stated that mordenite mineral types typically
possess a high percentage of Ca, and consequently, more Ca ions are exchanged in the contact solution.
Table 1. Elemental composition of the natural zeolite used in this experiment.
Elements Unit Cencentration
Si % 18.307
K % 3.466
Al % 2.754
Ca % 2.387
Fe % 1.992
Ti % 0.146
Sr % 0.122
Mg ppm 927.000
Zn ppm 428.900
Mn ppm 302.200
Ba ppm 202.400
Cu ppm 93.600
Rb ppm 84.800
Ni ppm 1.800
Equilibrium studies
Adsorption of Mn by natural zeolite
The natural zeolite used in this experiment had the capability to adsorb Mn ions from an aqueous solution.
The effects of zeolite quantity, thermal activation, and particle size on the rate of Mn adsorption by natural zeolites at two different initial pH solutions are presented in Table 2 and Table 3, respectively.
Open Access 4195 Table 2. Effects of the zeolite quantity, thermal activation, and particle size on Mn adsorption from the solution
with initial pH of 5.5 (mg g-1).
Zeolite (g) 25 oC 250 oC
<0.5 mm 1-2 mm 2-4 mm <0.5 mm 1-2 mm 2-4 mm
0.5 4.25 4.33 4.24 4.37 4.33 4.29
1.0 2.28 2.36 2.20 2.23 2.23 2.17
1.5 1.59 1.62 1.52 1.56 1.59 1.51
2.0 1.22 1.23 1.21 1.20 1.21 1.18
2.5 0.98 0.99 0.97 0.97 0.98 0.95
3.0 0.82 0.83 0.82 0.81 0.82 0.81
3.5 0.71 0.71 0.70 0.70 0.71 0.70
4.0 0.62 0.62 0.62 0.61 0.62 0.62
4.5 0.55 0.55 0.55 0.55 0.55 0.55
5.0 0.50 0.50 0.49 0.49 0.50 0.49
Table 3. Effects of the zeolite quantity, thermal activation, and particle size on Mn adsorption from the solution with initial pH of 7.0 (mg g-1).
Zeolite (g) 25 oC 250 oC
<0.5 mm 1-2 mm 2-4 mm <0.5 mm 1-2 mm 2-4 mm
0.5 4.92 4.57 2.58 4.79 4.9 4.76
1.0 2.47 2.41 2.35 2.47 2.49 2.49
1.5 1.66 1.66 1.66 1.66 1.66 1.66
2.0 1.25 1.25 1.25 1.24 1.25 1.24
2.5 1.00 1.00 1.00 1.00 1.00 1.00
3.0 0.83 0.83 0.83 0.83 0.83 0.83
3.5 0.71 0.71 0.71 0.71 0.71 0.71
4.0 0.62 0.62 0.62 0.62 0.62 0.62
4.5 0.55 0.55 0.55 0.55 0.55 0.56
5.0 0.50 0.55 0.50 0.50 0.50 0.50
Data in both Table 2 and Table 3 show that even in the lowest quantity (0.5 g), the natural zeolite was able to remove the highest amount of Mn from the solution (>4.00 mg g-1), compared to larger amounts of zeolites regardless of the size of the particles, thermal treatment, and the initial pH of the solutions. Both tables indicate that adsorbed Mn per unit zeolite mass consistently decreased with increasing the amount of zeolite mass. This was probably due to the presence of exchangeable Ca and other cations in the zeolite materials, which had competed with Mn ions from the solution for zeolite surfaces, causing low adsorbed Mn. Both tables also show that the effects of particle size of the natural zeolites and thermal activation were relatively small compared to those of the initial pH of the solutions. Similar findings have been reported by other authors. Wahono et al. (2021) reported that mordenite zeolite has high thermal stability, and the effects of temperature were not found until the temperatures were above 600 oC. An increase in initial pH solutions from pH 5.5 to 7.0 slightly increased the amount of adsorbed Mn to the natural zeolite, particularly at 0.5 to 2.0 g zeolite mass, regardless of the sizes and thermal treatments of the zeolites. An increase in pH had possibly caused an increase in the number of negative charges, resulting in the slightly higher retention capacity of the natural zeolites.
Freundllich and Langmuir isothermic models The Mn adsorption on the natural zeolite can be described in the Freundlich and Langmuir parameters as presented in Table 4 and Table 5, respectively. The Kf, 1/n, and R2 values in Table 4 were calculated after plotting the log Qe against log Ce of equation 2 on the isothermic graphs. Table 4 shows all Kf values were positive and consistently much higher in the suspensions with initial pH of 5.5 conditions, 0.66 to 1.16 mg g-1 compared to 0.06 to 0.26 mg g-1 at the initial pH of 7, indicating a stronger Mn adsorption at more acidic conditions. Similarly, slightly higher R2 values were found almost in all more acidic environments (original pH 5.5), regardless of the thermal treatments as well as zeolite mass. Normal 1/n values are in the ranges of 0.1 to <1, which indicates favorable adsorption (Omri and Benzina, 2012), whereas all 1/n values obtained in this study were >1.
Dada et al. (2012) and Kwakye-Awuah et al. (2019) stated that 1/n above >1 suggests a cooperative adsorption phenomenon. Based on his experiment, Liu (2015) explained in this type of adsorption, there were interactions between adsorbates or between adsorbate and adsorbent, which caused a deviation from uniform interactions. Therefore, the adsorption occurring in this experiment was not an ideal Langmuir adsorption
Open Access 4196 process for Mn as commonly monolayer coverage of
adsorbent sites (Dada et al., 2012; Neag et al., 2020).
Furthermore, Liu (2015) suggested that in cooperative
adsorption, there was multi-layer or apparent multi- layer behaviour of adsorption on the surface of adsorbents.
Table 4. Freundlich isothermic parameters of Mn adsorption on natural zeolite.
Zeolite ø (mm) Temperature Initial Solution pH Freundlich Model**)
Kf 1/n R2
<0.5 25 oC 5.5 1.08 1.41 0.99
7.0 0.17 1.00 0.82
250 oC 5.5 1.55 1.19 0.95
7.0 0.19 1.37 0.96
1-2 25 oC 5.5 0.63 1.58 0.99
7.0 0.11 2.06 0.79
250 oC 5.5 0.98 1.59 0.97
7.0 0.10 1.16 0.93
2-4 25 oC 5.5 1.55 1.36 0.93
7.0 0.26 2.71 0.71
250 oC 5.5 1.86 1.28 0.89
7.0 0.06 2.14 0.96
**) Kf = Freundlich adsorption constant (mg g-1), related to the strength and amount of adsorption; 1/n = adsorption intensity (n<1= adsorption with chemical interaction); R2 = coefficient of correlation.
The Qm, KL, and R2 values in Table 5 were obtained after plotting the 1/Qe against 1/Ce data in the isothermic Langmuir model of Equation 4. Unlike the Freundlich equation, almost all KL and Qm values in the Langmuir equation were negative, except the Qm values from zeolites of 2 mm that were heated to 250
oC and with higher initial pH (7.0) solutions which counted 0.42 mg g-1. As stated earlier, the adsorption mechanisms of Mn on this particular natural zeolite was cooperative adsorption, which means that there were interactions between adsorbate (Mn ions) and the zeolite, which had caused deviations from uniform interactions, as assumed in Langmuir isothermic equations. Similar to the Freundlich model, all R2 values of Langmuir equations tended to be higher in acidic environments (pH 5.5), from 0.92 to 0.98, than
in the higher initial pH (7.0) solutions, from 0.64 to 0.88, regardless the thermal treatments and zeolite mass. In general, the R2 values of the Freundlich isothermic were 0.71 to 0.99 (Table 4); they were slightly higher than those of the Langmuir isothermic model, 0.64 to 0.98 (Table 5), indicating that Mn adsorption by natural zeolites fitted to the Freundlich model over the Langmuir model. In addition, negative values of most Qm and KL in the Langmuir data (Table 5) confirmed that Mn adsorption behaviour did not follow the Langmuir model. Figure 1 also shows that the natural zeolites used in this study were heterogeneous adsorbent with porous structures, indicating that the adsorption of Mn had taken place at the surface of the zeolite as well as in the inner parts of the structures (pore spaces), as discussed above.
Table 5. Langmuir isothermic parameters of Mn adsorption on natural zeolite.
Zeolite ø (mm) Temperature Initial Solution pH Langmuir Model***)
Qm KL R2
<0.5 25 oC 5.5 -3.90 -0.26 0.98
7.0 -29.85 -0.03 0.75
250 oC 5.5 -4.90 -0.20 0.95
7.0 -0.99 -1.01 0.80
1-2 25 oC 5.5 -1.96 -0.51 0.97
7.0 0.42 2.37 0.64
250 oC 5.5 -1.41 -0.71 0.96
7.0 -1.19 -0.84 0.85
2-4 25 oC 5.5 -3.90 -0.26 0.96
7.0 -0.75 -1.34 0.86
250 oC 5.5 -3.50 -0.28 0.92
7.0 -0.08 -12.85 0.88
***) Qm= Maximum adsorption capacity (mg/g); KL = Langmuir constant related to binding energy; R2 = coeficient of correlation.
Open Access 4197 This finding was also reported by Kwakye-Awuah et
al. (2019). They suggested that the mechanism of the sorption of Mn to zeolites was attributed to both the ion exchange and adsorption processes. During the ion exchange process, Mn not only moved through the pores of the zeolite mass but also through channels of the lattice, replacing exchangeable cations (mainly sodium, potassium, and calcium). Kwakye-Awuah et al. (2019) also found that the Langmuir equation did not provide a good fit for the adsorption of Mn to zeolites synthesized from bauxite and kaolin, with R2 values of 0.66 and 0.98 derived from Langmuir and Freundlich models respectively.
Conclusion
Equilibrium studies showed that natural zeolites were capable of removing Mn ions from aqueous solutions.
Scanning Electron Microscopy evidenced the presence of a porous structure of the natural zeolites, which had caused adsorption processes on the surface as well as in the inner parts of the zeolite structure. The natural zeolites tended to remove more Mn in the initial neutral environment (pH 7.0) compared to the acidic one (pH 5.5), regardless of the size of the particles and thermal treatment. The Freundlich isothermic model, however, appeared to describe Mn adsorption behaviour better than the Langmuir model on the mixed clinoptilolite and mordenite zeolite types from West Java, Indonesia, especially in the slightly acidic condition, as indicated by higher R2 values. In conclusion, the natural zeolite used in this experiment is a promising material to remove Mn from an aqueous solution such as acid mine drainage (AMD), particularly as a downstream treatment when all acid metals such as Al and Fe have been removed.
Acknowledgements
The authors thank the Research and Extention Institute (LPPM), UPN “Veteran” Yogyakarta, for funding this Internal Research Project through the Cluster Scheme. The authors also thank Mr. Aris Purwanto, Ms. Sinta Sinaga, and Ms. Bekti Atuti for their fruitful help in the Laboratory Analysis.
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