Abstract:
In this present study aimed to determine and compare the potential of different weights of activated bentonite (BN), as a useful adsorbent for the removal of copper sulfate from aqueous systems. The bentonite was chemically activated with 1M solution of ammonium chloride (bentonite: NH4CL ratio; 1:1, w/w). UV-VIS spectrophotometry was used to investigate the adsorption ability of activated natural materials (BN) to adsorb copper sulfate (CuSO4·5H2O). Raw bentonite BN (non- heated), possesses adsorption properties towards elimination of copper (II) ions from its aqueous solutions. The Cu2+ removal efficiency of BN was approximately 62 %, but it has been noticed that the copper sulfate removal efficiency increases with as heating temperature of bentonite increases not more than 200 C with proportion of 69% of removal. The removal percentage of copper (II) was increased to reach out 90% after (BN) exposed to thermal treatment. These maximum values of rate were obtained when the dosage of bentonite is 0.4g/100mL.
1. Introduction
The presence of heavy metals in aquatic ecosystems is of growing concern due to their
relatively high toxicity. Human activity causes a great deal of heavy-metal water contamination.
In fact, the concentration of lead in areas affected by humans is 20 times greater than in
unpolluted regions not directly impacted by human activity [1]. Therefore, several laws and
regulations designed to reduce effluence with heavy metals. The Environmental Protection
Agency, a federal institution tasked with monitoring and controlling the discharge of pollutants
into the environment, has established the maximum allowable emissions for heavy metals as:
lead 15 ppb, copper 1.3 ppm, mercury 2 ppb, cadmium 5 ppb, and chromium 100 ppb (EPA).
Copper is the most prevalent metal, as it is used in industrial production, metal mechanic
factories, and even food production. Despite the laws created to limit pollution, excess copper
still exists in many bodies of water, making it important that we find methods to safely remove
it.
The objective of this study was to investigate the efficiency of natural adsorbents-bentonite (BN) as an adsorbent material, in CuSO4 adsorption from aqueous solution. Using batch adsorption studies, the influence of the adsorbent’s dose, and the usage rate of (BN).
2. Literature Review
The contamination of water resources due to the disposal of heavy metal ions has been an
increasing worldwide concern for the last few decades. It is well known that some metals are
poisonous to human lives and ecological environments. Copper sulfate is an inorganic compound that combines sulfur with copper, and it accumulates as a heavy metal precipitate once it is applied to water. Copper is an essential micronutrient to humans and other life forms with extensive roles in enzyme activities. Nevertheless, it is considered one of the toxic metals to human beings as excessive copper exposure causes serious mental and neurological illnesses including schizophrenia, depression, autism, tardive dyskinesia, and memory loss; and Continue exposure of copper by humans leads to hepatic and renal dysfunctions, hypertension, gastrointestinal irritation, and most types of cancer. The use of large amount and a wide variety of copper-based agrochemicals is likely to lead to the contamination of the neighboring water resources, thus affecting their quality in terms of chemical and ecological status. Many people in rural Africa may be exposed to copper sulfate and its toxicities, often through exposure while farming. Many cases of accidental intoxication with copper sulfate have been reported among farmworkers who absorbed large amounts of the substance through the skin. Hence, health care providers must be able to identify and treat copper sulfate poisoning.
By the increasing discharge of industrial wastewater, copper was listed as one of the most
widespread heavy metal contaminants. Thus far, various techniques have been used to remove
water contaminations, such as salts, heavy metals, organic contaminants, and other
contaminations; including ion-exchange, electrocoagulation, membrane separation, reverse
osmosis, electrodialysis, solvent extraction, packed bed filtration. These techniques are usually
not economical due to their energy dependence and high costs, especially for agricultural
purposes, which is the biggest water consumer in the world. Further, some of these methods
produce chemical byproducts that may threaten the organisms that inhabit these ecosystems. In
contrast, the adsorption technique is one of the preferred and promised methods because of its
high efficiency and low cost for the removing ionic species from water resources.
Different research groups have studied removal of CuSO4 from water using adsorption
process. In this research study made by Boukerroui Abdelhamid et al, used un-treated bentonite (BN) waste and observed percentage of Cu removal increased from 15 to 69% when the adsorbent dose per 100 ml of solution was increased from 0.25 to 1g. In another study, the maximum adsorption percentage for the removal of copper (II) by H3PO4-treated rice husk was 88.9% [11]. In some other previous works, dried sugar beet pulp has been used successfully as an adsorbing agent for the removal of copper (II) ions from aqueous solutions [12]. Moreover, Walnut shells have been studied for removal of copper ions from aqueous solution by researchers, and the highest removal efficiency of copper ions obtained was 79.54 %, at dose 0.5 g / 50 mL of solution.
To investigate the adsorption ability of activated natural materials (BN) to adsorb Copper Sulfate (CuSO4·5H2O), UV-VIS spectrophotometry was used. The color of a species is representing its ability to absorb specific wavelengths of light, and copper sulfate (CuSO4) compounds tend to be blue in color. Lower wavelengths of light which correspond to the blue color and absorb better at higher wavelengths of light. This was supported by the results of the research. The wavelengths of light, which are absorbed are determined by the electrons in that species. As electrons move around, they can absorb energy and become agitated. The type of
atoms found in the compound and the bonds that connect those atoms determines the energy and
wavelength of light the electrons absorb. As the solution color becomes darker and more
concentrated, the concentration increases. Increasing concentration leads to more electrons in the
sample, which can then absorb more light at a specific wavelength. The relationship between the
concentration of the species and its absorbance is best determined using a wavelength of light in
a region of the visible spectrum where the maximum absorbance is observed. This wavelength is
known as λmax, and it is most sensitive to the concentration change.
Natural waste materials, such as bentonite clay (BN) has been studied by various researchers to investigate their effectiveness in removing ions and metals from aqueous solutions. Most commonly used adsorbents are untreated/unmodified; however, in this study, the major objective of the study was to explore the potential of acid-modified (NH4CL) bentonite in the removal CuSO4 from its aqueous solution.
3. Material and method
3.1. Materials
3.1.1. Ultrapure Reverse Osmosis (RO) Water
In this research study, RO waters were used to evaluate the adsorption capacity of activated of the natural materials (BN). The conductivity value of (BN) waters was recorded between 1.0-1.2 S/cm @ 25°C.
3.2. Chemicals
In this research study, copper sulfate (CuSO4) was used to evaluate the adsorption capacity of
activated bentonite for ammonium chloride. Various concentrations (1,2,3,4,5) g/ of (BN) were used to examine their effectiveness in binding CuSO4 from aqueous solution. Below lists of sorbent natural materials and all the chemicals used in this study.
3.2.1. Copper Sulfate (CuSO4·5H2O) Solution
Copper sulfate pentahydrate (CuSO4·5H2O) was used to prepare a stock solution of 0.5 M
(CuSO4·5H2O) (Fisher Chemical, NJ, USA) by adding 62.42 grams of CuSO4·5H2O to ultrapure water (RO water) in a 500 ml volumetric flask. The electrical conductivity and TDS of this 0.5 M solution were 30.6 mS/cm and 15.1 ppt at 21.8°C, respectively.
3.2.2. Ammonium Chloride (NH4CL)
Ammonium Chloride (NH4CL) was used in this study to modify the efficiency of bentonite clay (BN) waste adsorption of copper sulfate from aqueous solutions. The dried (BN) waste was activated by mixing with NH4CL (BN waste: NH4CL ratio; 1:1, w/w) and keeping it in a fume hood at 60◦C for 6 days.
3.2.3 Nitric Acid
Pure compound colorless Nitric Acid (HNO3) was used in this study as cleaners for the
glassware and plastic materials used. All glassware and plastic materials used were rinsed by the
nitric acid solution before use then cleaned repeatedly with distilled/deionized water.
4. Laboratory Equipment
4.1. Thermo fisher Scientific
The ultrapure water (RO Water) that used in this research study was provided by
(Thermo scientific Barnstead smart2pure ultrapure water system, Thermo fisher
Scientific, CA, USA). This system works at pressure range of 1-6 bar, feed water
temperate between 2-35°C and PH between 4-11. Figure.1 shows the Thermo scientific
Barnstead smart2pure ultrapure water system.
Fig.1.Thermo scientific Barnstead smart2pure ultrapure water system, Thermo fisher Scientific, CA, USA
4.2. Portable Waterproof Conductivity Meter
A Fisher Scientific Accumet AP75 Portable Waterproof electrical conductivity meter (Fisher
Scientific, Singapore) was used to examine the adsorption of total dissolved solids or salts by the
natural materials (BN) activated in this study. The conductivity meter device measures
any change in the conductivity and TDS by immersing the probe in the solution beyond the
upper steel band. Then, stir the probe gently to create a homogeneous sample and allow time for
the reading to stabilize. Figure 2 shows the conductivity meter that used in this research study
Fig.2. Accumet Fisher Scientific AP75 Portable Waterproof Conductivity Meter. (Fisher Scientific, Singapore)
4.3. Forced Air Oven
A Forced Air Oven (1370 FM forced air oven, VWR scientific products, AZ, USA) was used in
this research study to determine the Moisture consents of the sorbent materials (BN). It was used by placing the sorbent sample (BN) in the oven to dry at various time and temperature. Figure 3 shows the Forced Air Oven that used in this research study.
Fig. 3. 1370 FM forced air oven, VWR scientific products, AZ, USA
4.4. Rotary Mixer (Boekel scientific Hybridization Oven)
A rotary mixer (Boekel scientific Hybridization Oven. PA, USA) is designed to provide rapid
heat-up, excellent temperature stability, and efficient mixing of materials. It was used by placing
the sample villas in the mixer at 40 rpm for 24 hrs at 23±2ºC to make sure the samples reached
equilibrium. Figure 4 shows the Rotary Mixer that used in this research study.
Fig. 4. Rotary Mixer (Boekel scientific Hybridization Oven., PA, USA)
4.5. UV-VIS, Spectrophotometer
The spectrophotometer (RED TIDE USB650, Ocean Optics. FL, USA) is used to determine the molar absorption of CuSO4 solution samples that were mixed with bentonite clay. The spectrophotometer was connected to software installed in the lab computer and used by preparing five standard concentration of CuSO4 solution (M). By measuring the absorbance of each standard at a specific wavelength (nm), a linear calibration equation can be produced to determine the unknown copper sulfate concentration in the solution. Figure 5 shows the Spectrophotometer that used in this research study.
Fig. 5. RED TIDE USB650, OceanOptics. FL, USA
4.6. Fisher Scientific accumet Meters
Fisher Scientific accumet Meters (Fisher Scientific accumet Meters AR15 pH/mV/°C Meter, International Equipment Company. MA, USA) was used to measure the pH of water sample solutions. Figure 6 shows the Fisher Scientific accumet Meters.
Fig. 6. Fisher Scientific accumet Meters. FL, USA
4.7. Analytical balance (Mettler Toledo Laboratory Balance)
In this research study, Mettler Toledo Laboratory Balance (MS204S,MettlerToledo,Switzerland) was used to prepare all water sample solutions with the molarity needed, adding the Activated natural material (BN) with accurate quantities and all other quantity measurements. Figure 7 shows the Mettler Toledo Laboratory Balance that used in this research study.
Fig. 7. Mettler Toledo Laboratory Balance (MS204S, Mettler Toledo, Switzerland)
4.8. Vulcan Multi-stage Programmable Furnace
After drying the sorbent samples for 24 hours at 100°C in the forced air oven, all samples (BN) must place in a furnace at different temperatures and 1-hour fixed time starting with 100 C and end up with 500 C (Furnace Vulcan 3-550, Dentsply International Inc., PA, USA). Figure 7 shows the Furnace Vulcan that used in this research study.
Figure 7. Furnace Vulcan 3-550, Dentsply International Inc., PA, USA
5. Methods
5.1. Thermal Treatment of Bentonite Impregnated by NH4Cl (1M)
The raw bentonite was crushed and sieved several times over 50 μm screen. This no-treated solid was noted as BN. A part of this pre-treatment BN was impregnated into 1M NH4Cl solutions with the bentonite / NH4Cl solutions ratio of 1:1 w/w. The suspension was left overnight at the ambient temperature under constant stirring, then dried in an oven at 60 °C for several days without washing. The dried material, after a fine crushing, was put in porcelain crucibles and heated in a furnace with controlled temperature values ranging between 100 and 500°C at 1-hour fixed period of times. The BN clay samples, heated at 100°C, were placed in the furnace for the different exposition temperature: 100; 200; 300; 400; 500 °C. After cooling, each bentonite sample was washed with distilled water (RO water) until all chloride ions were removed. These materials were crushed and sieved over 0.05 mm screen. The bentonite obtained was noted as BA and used to investigate its Cu2+ removal ability.
5.2. Removal of Copper (II) by Bentonite
In a 250 mL polyethylene bottles, a mass of m (g) activated bentonite (BA) or raw bentonite (BN) was dispersed into 100 mL of copper solution with initial concentration (C0) 0.1 (mg L-1). The pH of suspensions varies between 5.5 and 6 (natural pH of suspensions). The suspensions were centrifuged after continuous stirring and the concentration of Cu2+ at the equilibrium state, final concentration (Ce) (mg L 1), where the supernatant was measured, was obtained.
5.3. Effect of the Physicochemical Parameters
The determination of optimum experimental conditions, for bentonite treatment and metal removal, were systematically through the study of following parameters:
· Temperature and duration of heating in oven.
· Contact time of bentonite-copper (II) solution mixture.
· The effect of clay titration (g bentonite / 100 mL copper (II) solution).
· Temperature influence on the adsorption of copper (II) ions.
6. Batch adsorption studies
In a batch experiment, triplicate vial samples were prepared. A dry mass of the activated natural sorbent materials (BN) were added in samples’ vials to obtain 0.25, 0.5, 0.75, 1, or 15 g/l doses of the adsorbents. An initial concentration of 0.2 M CuSO4 solution was used in experiments by adding 7.6 ml of 0.5 M CuSO4 solution to sample vials. The mixture was then mixed in a rotary shaker set at 25ºC for 24 hrs. to make sure the samples reached equilibrium. After equilibrium, all vials were filtered by using a syringe filter to separate the liquid phase from the solid phase. Moreover, 10 mL of the liquid phase from each sample was obtained to measure the CuSO4 concentration using a spectrophotometer. Following the sample analysis, the measured values were compared to the initial values, and the measurement of equilibrium adsorption, qe, was calculated for each does.
7. Chemical Quantification Methods
7.1. UV-VIS Spectrophotometry (RED TIDE USB650, Ocean Optics. FL, USA)
To investigate the adsorption ability of activated natural materials (BN) to adsorb Copper Sulfate (CuSO4·5H2O), UV-VIS spectrophotometry was used. A 0.50 M CuSO4 stock solution was prepared to evaluate the absorption capacity of the absorbent samples for copper sulfate removal. Five additional standard CuSO4 solutions 0.1, 0.2, 0.3, 0.4, and 0.5 M were prepared for analysis by diluting the 0.50 M CuSO4 stock solution using ultrapure (RO water) (Table 1). Comparing to the absorbance value of 0.50 M CuSO4 solution on ”Using Absorbance to Determine the Concentration of CuSO4”, this research study selected a 638 as the maximum wavelength. As the absorbance at 638 of the CuSO4 standard solutions were directly proportional to their concentrations (Table 1, Figure 8), the linear calibration equation (y = 2.324x + 0.02) obtained for the graph can be used to determine the unknown CuSO4 concentration of any sample to evaluate the absorbance efficiency of the activated natural materials (BN). A calibration curve was developed using standards at each time experimental samples were examined.
Table 1. CuSO4 standard solutions and their absorbance at 638 nm.
| Concentration of Standard CuSO4 Solution (M) | Absorbance at 638 nm |
| 0.1 | 0.245 |
| 0.2 | 0.457 |
| 0.3 | 0.655 |
| 0.4 | 0.859 |
| 0.5 | 1.052 |
Figure 8. Determination of molar absorptivity of CuSO4
Calculation of how this paper used the linear calibration equation (y = 2.016x + 0.0488) to determine the unknown copper sulfate concentration is illustrated in Appendix B.
8. Conclusion
The heating of raw bentonite impregnated in 1 M ammonium chloride solutions in the oven renders it possibility to create from new sites of ion exchange and this leads to an increase of the adsorption capacity of copper (II) ions from their aqueous solutions with pH=6 using bentonite, obtained from Maghnia (west Algeria). This thermal treatment improves the affinity of this material towards the copper ions adsorption while, a process of a spontaneous equilibrium is established as soon as the contact is made between the copper (II) ions on the surface of clay particles in aqueous solutions. The study of adsorption isotherms shows that the removal efficiency of Cu2+ ions is governed by the two traditional models; Langmuir and Freundlich, with which the adsorption mechanism of Cu2+ ions by bentonite is a phenomenon of ionic exchange. This thermal treatment of bentonite inhibited the temperature effect of the aqueous solutions towards the removal rate of Cu2+ ions and also the improving of the Kd values. Owing to this new activation technique, applied for the clay materials, a rational use of bentonite could be envisaged in the treatment of wastewaters often polluted by the heavy metals. Thus, this work may be considered as a modest contribution to minimize the quantities of sludge during the decontamination of industrial effluents containing the heavy metals such as the family of copper (II).
Concentration (m) VS. Abs (AU)of Copper
Abs
0.1 0.2 0.3 0.4 0.5 0.245 0.45700000000000002 0.65500000000000003 0.85899999999999999 1.052
Copper Sulfate Concentration (m)
Absorbance (AU)