Adsorptive removal of heavy metals from water using thermal treated laterite: an approach for purification of rain water
| Meeting | VIWC2026 |
| Topic | OS4: Water quality and Aquaculture |
| Author | Dinh-Trinh Tran | Duc-Toan Vu | Manh-Cuong Le |
| Organization | VNU Key Lab. of Advanced Materials for Green Growth, University of Science, Vietnam National University | Research of Organic Matter (ROOM), Environmental and Life Science Research Laboratory, Thuyloi University, Vietnam | Faculty Building Material, Hanoi University of Civil Engineering, Ha Noi 100000, Vietnam. |
| ID | 2023.1676261918 |
Content
1. Introduction
The heavy metal pollution raised global concerns in recent decades due to its negative impact to human health and environment. Due to the high stability of heavy metal species, heavy metals could be absorbed by plants and animals, then accumulated in human bodies, causing heavy metal induce (Koedrith et al, 2013). Previous studies showed that most heavy metals are carcinogens in different body parts such as kidney, blood, bones and nervous system. Several methods were developed to remove the heavy metals in aqueous solutions. Each method had its own advantages and drawbacks. Among these methods, adsorption is a simple, selective and effective method. There were hundreds of absorbents for heavy metals including natural material and its derivatives like zeolites, clay materials, laterites; carbon-based materials…The application of natural materials in the removal of heavy metals and purification of drinking water is increasingly gaining attention. But the performance of heavy metal adsorption of raw materials has been found to be limited, due to its low specific surface area as well as low porosity. They required further modification and/or treatment to enhance the adsorption capacity. Laterite, naturally available, is a natural rock that could be used for the adsorption of heavy metals and drinking water purification as it contains minerals. This research aims to produce thermal treatment laterite for heavy metals adsorption and rain water purification.
In this work, the raw laterite was collected and modified by a thermal process. The obtained laterite was examined by different methods such as XRD, SEM/EDX, FT-IR, BET, pHpzc. Cu2+ and Ni2+ were chosen as model ions for adsorption study. The purification of rain water by modified laterite to produce drinking water was also evaluated.
2. Experimental
2.1. Activation of natural laterite
All chemicals were of analytical grade provided by Sigma Aldrich, and used without any further purification. Natural laterite collected from Thach That district, Hanoi, Vietnam was first grinded then sieved to obtain particles with the size range of 0.5-1.0 mm. The obtained samples were subsequently washed with distilled water, then dried at 105 ℃ for 48 h in an oven, prior to being heated under air environment at 500 °C for 6 h to remove organic materials remained in the raw laterite.
2.2. Characterization of materials
The crystal structure of materials was examined by a X-ray diffraction spectroscopy (XRD, D8 Advance – Bruker), composition and morphology of the samples were studied with the aid of a Scanning Electron Microscope (SEM) Nova NanoSEM 450, coupled with an Energy-Dispersive X ray spectroscopy (EDX), JED-2300 Analysis Station Plus. Surface functional groups were identified using a FT-IR spectroscopy, Jasco 4600, Japan. Nitrogen isothermal adsorption-desorption (Brunauer-Emmett-Teller-BET) was determined by TriStar 3000 V6.07 A. Concentrations of Ni2+ and Cu2+ ions were determined by an Atomic Absorption Spectrophotometer (AAS), Shimadzu AA-7000 F.
2.3. Batch experiments
For the adsorption of Ni2+, Cu2+, a typical batch experiment was conducted as follow: 100 mL of heavy metal with known concentration were transferred to a 250 mL conical flask. A known amount of treated laterite was added to the solution. The mixture was shaken for 2 h. To study the effect of contact time, 5 mL of the reaction solution was taken with an interval of 15 min. The solution was then filtered prior to be subjected to AAS to determine the remaining heavy metal contents. The pH value of solutions ranged from 2 to 12 to examine the impact of pH. The effects of adsorbent dose and initial metal concentration were studied with the same procedure, with the optimal pH. The adsorption isotherm study was carried out by fitting experimental data to Langmuir and Freundlich models. The kinetics of adsorption process were evaluated by pseudo-first order, pseudo- second order, and intramolecular models. Finally, modified laterite was deployed for purifying real rain water samples.
3. Results and discussion
3.1. Characterization of materials
The peaks at 2θ = 21º, 26º, 33º, 37º, 54º, 61º represented the presence of goethite in the structure of laterite. The peaks at 2θ = 24º, 35º, 49º, 62º, 64º in the modified laterite were associated with of hematite. The presence of quartz in the laterite structure was confirmed at 2θ =20º. FT-IR spectra showed that the band at 3406.29 cm-1 was assigned to -OH group of Si. The peaks at 1031.92 cm-1, 1036.84 cm-1, 912.33 cm-1, and 796.60 cm-1 were due to Si–O–Fe, Al–OH, Fe–OH vibrations. The Fe–O bonds stretching at 534.28 confirmed the presence of hematite (Pham et al, 2017).
Figure 1: XRD pattern (left) and FT-IR spectra (right) of raw and modified laterite samples.
Thermally treated laterite presented a clear prominent coating of fine particles on the surface (Figure 2 right) while raw one had a bulker and more heterogeneous surface texture and was visibly less porous (Figure 2 left). The presence of fine particles on surface of modified laterite could be attributed to the thermal decomposition of organic materials from raw laterite.
Figure 2: SEM images of raw (left) and modified (right) laterite.
The N2 adsorption-desorption diagrams of both raw (Figure 3a) and modified laterites (Figure 3b) are of type IV, and hysteresis loops are respectively of form H3 and H1 for treated and raw laterites. This suggests that both materials are shaped by mesoporous material. It is noted that the thermal treatment of laterites resulted in a decline in total surface area (24.87 m2/g for modified laterite vs 49.73 m2/g for raw laterite), conversely to average pore diameter and total pore volume. Indeed, average pore diameter of raw and treated laterites were respectively 3.47 nm and 12.2 nm while their corresponding pore volume were 0.0432 and 0.0756 cm3/g. This might be linked with the loss of porous organic materials on the surface of laterites when being heated at 500℃, leading to the changes in porous structure and decrease in surface area of laterite. Although, the thermal treatment of raw laterite led to decrease in its surface area, this process was really important to remove organic materials and others which could be released to treated water causing secondary pollution. The pHpzc of the treated laterite was 8.0, implying positive surface charge in solution having pH ≤ 8 while it was negatively charged in pH > 8 solutions.
Figure 3: Nitrogen adsorption–desorption isotherms and pore distribution of (a) raw and (b) modified laterite samples, (c) pHpzc of the modified laterite.
3.2. Adsorption experiments The results in Figure 4a shows that the removal efficiency increased with increasing contact time. 91.6 and 94.2 % of Ni2+ and Cu2+ were removed after 40 min, suggesting equilibrium time was 40 min. The optimal pH was around pH 7.0 as when it went above 8 there was precipitation of Ni2+ and Cu2+, leading to higher removal efficiencies but it was not linked to the adsorption process.
Figure 4: Impacts of contact time (a), (b) pH, (c) adsorbent load, and (d) initial concentration on the adsorption capacity/efficiency of treated laterite.
The equilibrium adsorption was analyzed using the Langmuir and Freundlich isotherm models. The validity of the isotherm models can be estimated by using their linearized plots (Figure 5). The Langmuir isotherm model described the best the Ni2+ and Cu2+ adsorption (R2>0.99), implying monolayer adsorption. The maximum uptake for Ni2+ and Cu2+ were respectively 10.3 mg/g and 8.1 mg/g. The results in this research show that the combination of laterite with sand and SODIS method allowed to safely removal turbidity and contaminants, including pathogens to produce water reaching Vietnam national standard for drinking water (QCVN 01:2009/BYT).
Figure 5: Langmuir (left) and Freundlich (right) model plots.
4. Conclusions Natural laterites collected from Thach That, Hanoi, Vietnam were successfully treated by thermal process to produce more stable materials. The results showed that treated laterites contained mainly mineral oxides and SiO2, Al2O3, which are suitable for purifying water to produce drinking water. The adsorption study revealed that the adsorption processes occurred quite fast, with the equilibrium time of 40 min. The heavy metal adsorption followed the Langmuir isotherm model, with the maximum uptakes of 10.3 mg/g and 8.1 mg/g for Cu2+ and Ni2+, respectively. The application of treated laterite also indicated that it could be used in combination with natural sand and SODIS method to safely produce drinking water from rain water. 5. Reference- Koedrith, P et al. (2013). Toxicogenomic approaches for understanding molecular mechanisms of heavy metal mutagenicity and carcinogenicity. Int. J. Hyg. Environ. Health. 216, 587–598.
- Pham, T.D et al. (2017). Adsorptive Removal of Copper by Using Surfactant Modified Laterite Soil. J. Chem. https://doi.org/10.1155/2017/1986071.
