paraphrasing

Many researchers have investigated the efficiency of natural waste materials like bentonite clay (BN) to determine their effectiveness of removing metals and ions from aqueous solutions. Most of these adsorbent materials are unmodified or untreated. However, this study was explored the potential of an acid-modified (NH4CL) bentonite in removing copper sulfate from aqueous solutions.

3.0 Materials and Methods

3.1 Materials

3.1.1Ultrapure Reverse Osmosis (RO) Water

3.2 Chemicals

In the same research, copper sulfate (CuSO4) was utilized to confirm the potency of adsorption of bentonite, which was activated using ammonium chloride. The concentration was varied in steps of 0.1, 0.2, 0.3, 0.4, and 0.5 concentration of BN to evaluate their efficiency in removing CuSO4 from aqueous copper solutions. In this section, the natural adsorbents and the chemicals that were used in the study are listed.

3.2.1 Copper Sulfate (CuSO4:5H2O) Solution

A 0.5 M stock solution was prepared using copper sulfate pentahydrate (CuSO4:5H2O), a finding from Fisher Chemical, NJ, USA. The mixture was made by the addition of 62.42 grams of copper sulfate pentahydrate (CuSO4:5H2O) to RO waters in a volumetric flask. The 0.5 M solution had an electrical conductivity of 30.6 mS/ cm, and TDS was observed to be 15.1 ppt at a temperature of 21.8°C.

3.2.1 Ammonium Chloride (NH4CL)

This acid was used to alter the efficiency of adsorption copper sulfate (CuSO4) utilizing natural materials, bentonite clay from aqueous solutions. The dried BN was mixed with ammonium chloride acid to activate it in a ratio of 1:1, i.e., NH4CL: BN water; 1:1, w/w. The fume hood was kept at a temperature of 60°C for 6 days.

3.2.3 Nitric Acid (HNO3)

The plastic materials and glassware used in the experiment were cleaned using pure, colorless compound nitric acid (HNO3). Besides, the equipment was first rinsed using a solution of nitric acid before the test. They were also cleaned regularly in the course of the experimentation with RO water.

4.0 Laboratory Equipment

4.1 Thermo Fisher Scientific

In this research study, the ultrapure or RO water used in the experiment was obtained using a Thermo scientific smart2pure ultrapure water system (Thermo Fisher Scientific, CA, in the USA). The system was functioning at temperatures ranging from 2 to 35°C, pressures between 1 and 6 bars, and PH ranging from 4 to 11.

Figure 1: Thermo scientific Barnstead smart2pure ultrapure water system, Thermo fisher Scientific, CA, USA

4.2 Portable Waterproof Conductivity Meter

The adsorption of the dissolved salts or solids by activated natural materials (BN) used in the study was tested using a Fisher Scientific Accumet AP75 Portable Waterproof electrical conductivity meter (Fisher Scientific, Singapore). The conductivity meter device is used to measure TDS and conductivity by submerging a probe into the solution below the upper brim of the steel band. The solution is then stirred gently to form a homogeneous sample to allow time for the readings to alleviate.

Figure 2: Accumet Fisher Scientific AP75 Portable Waterproof Conductivity Meter. (Fisher Scientific, Singapore)

4.3 Forced Air Oven

The moisture contents of adsorbent materials (BN) activated was specified using a Forced Air Oven. The adsorbent material samples were placed in the oven to dry at varying temperatures and time.

Figure 3: 1370 FM forced air oven, VWR scientific products, AZ, USA

4.4 Rotary Mixer (Boekel Scientific Hybridization Oven)

This system was generated to give rapid heat-up, efficient mixing, and temperature stability. The samples were placed in villas at 40 revolutions per minute for 24 hours at a temperature of 23±2ºC to ensure the samples reached the equilibrium point. The rotary mixer used in this study is Rotary Mixer (Boekel scientific Hybridization Oven., PA, USA).

Figure 4: Rotary Mixer (Boekel scientific Hybridization Oven., PA, USA)

4.5 UV-VIS, Spectrophotometer

The molar absorption of the samples of copper sulfate (CuSO4) mixed with natural materials (BN) activated was identified in this research using spectrophotometry (RED TIDE USB650, Ocean Optics. FL, USA). This spectrophotometry was interconnected with a computer in the laboratory to display the results. Five standard samples of varying concentrations (M) of copper sulfate were used in the study. The equation for linear calibration can be used to determine the concentration of CuSO4 solution, which is unknown in the experiment. This equation is determined by measuring the efficiency of adsorption at a certain wavelength (nm).

Figure 5: RED TIDE USB650, OceanOptics. FL, USA

4.6 Fisher Scientific Accumet Meters

This equipment was used in measuring the pH of the solutions of sample water. Figure 6 below shows the Fischer scientific accumet meters used in this research study is Fisher Scientific accumet Meters (Fisher Scientific accumet Meters AR15 pH/mV/°C Meter, International Equipment Company. MA, USA).

Figure 6: Fisher Scientific accumet Meters. FL, USA

4.7 Analytical Balance (Mettler Toledo Laboratory Balance)

The water solutions at required molarity, quantities of activated materials (BN), and other measurements on quality were identified using an analytical balance in this study. A Mettler Toledo Laboratory Balance (MS204S, Mettler Toledo, Switzerland) was used in this particular study.

Figure 7: Mettler Toledo Laboratory Balance (MS204S, Mettler Toledo, Switzerland)

4.8 Vulcan Multi-stage Programmable Furnace

As we have seen in the previous section, the samples of adsorbent materials (BN) were placed in a forced-air oven at 100°C for 24 hours. From here, the samples are placed in a furnace with temperatures varying between 100 °C and 500 °C. The used in this study is shown below:

Figure 8: Furnace Vulcan 3-550 (Dentsply International Inc., PA, USA).

5.0 Methods

5.1 Thermal Treatment of Bentonite Impregnated by NH4Cl (1M)

First, raw bentonite clay (BN) was crushed into small pieces before sieving it several times over a screen with holes of a diameter of 50 μm. The residue was labeled as BN. Some of this untreated BN was saturated with 1M NH4CL at a ratio of 1: 1, i.e., NH4CL solution: bentonite; 1:11 w/w. This suspension was suspended overnight at ambient temperatures and stirred continuously. The solid was then dried without washing in an oven at a temperature of 60 °C. After drying and crushing the solid into fine particles, it was placed in porcelain crucibles for heating in a furnace at temperatures ranging from 100°C to 500°C in periods of 1 hour. The samples of bentonite were exposed to temperatures of 100; 200; 300; 400; 500°C. After that, the bentonite was cooled and washed using distilled water to rid of all chloride ions. These materials were again crushed and sieved over a screen with 0.05 mm. The samples obtained after sieving were labeled BA, which was used in the investigation of the removal ability of Cu2+ using bentonite.

5.2 Removal of Cu2+ by Bentonite

A mass of BN or BA m (g) was dispersed in polyethylene bottles of 250 ml into a solution of copper at a concentration (C0) 0.1(mg L-1). The pH of these suspensions ranged in the values of natural suspensions pH of 5.5 and 6. Through continuous stirring, the suspensions were centrifuged, and Cu2+ concentration at the final concentration (Ce) (mg L 1) was measured at this point.

5.3 Effects of the Physiochemical Parameters

The optimum conditions of the experiment were specified while the efficiency of metal removal and treatment of bentonite was systematic throughout this study as it followed the required parameter i.e.

· Duration of heating and oven temperatures

· Exposure time for bentonite to Cu2+ solutions

· Clay titration effects, i.e., g bentonite per 100 ml of copper (II) solution

· Influence of heating on the rate of adsorption of Cu2+

6.0 Batch Adsorption Studies

Triplicate flask samples were prepared for a batch experiment. A mass of dry adsorbent material (BN) activated was added in vials to get 0.25, 0.5. 0.75,1 Or 15g/l dosages of adsorbents. The CuSO4 solution at 0.2 M was made in the experiment through the addition of 7.6 ml of CuSO4 at 0.5 M to these sample vials. This mixture was thoroughly mixed using a rotary shaker at a temperature of 25ºC for 24 hours to ensure the samples reach equilibrium points. Once the equilibrium was reached, the vials a syringe filter was used to separate the solids from the liquid. About 10 ml of the filtrate from each set up was used in determining the concentration of CuSO4 using a spectrophotometer. Through sample analysis, the values obtained were equated to the initial data. Besides, the equilibrium adsorption (Qe) for each of the samples was calculated.

7.0 Chemical Quantification Methods

7.1 UV-VIS Spectrophotometry (RED TIDE USB650, Ocean Optics. FL, USA)

The ability to naturally activated (BN) to absorb copper ions from the solution of copper sulfate (CuSO4-5H2O) was studied using a UV-VIS spectrophotometry. An initial stock solution of CuSO4 with a concentration of 0.05M was prepared for usage in the investigation of the absorption ability of the absorbent samples. The other five additional solutions at 0.1, 0.2, 0.3, 0.4, and 0.5 M were prepared by diluting the initial solutions with distilled water or RO water. For purposes of comparison and using concentration to determine absorbance, the maximum wavelength in this study was set at 638 nm.

Assuming that the absorbance and concentration at this wavelength were directly proportional, then a linear equation for calibration y = 2.324x + 0.02 was used. The graph can be used to determine the concentration of CuSO4 of each sample and the efficiency of absorbance of each activated bentonite (BN). A curve was also obtained for calibration at various time instances. The results from this experiment are tabulated in Table 1 below:

Table 1: CuSO4 solutions and their respective absorbance at 638nm

A graph of absorbance against the concentration of copper sulfate is shown in figure 9 below:

Figure 9: Determination of molar absorptivity of CuSO4

From the graph, an equation y = 2.016x + 0.0488 was obtained that can be used to determine the unknown concentration of copper sulfate solutions.

8.0 Conclusion

Heating of raw bentonite (BN) soaked in a concentrated solution of ammonium chloride in an oven increases the ion exchange sites in the material, which in turn leads to increases in the capability of absorption of Cu2+ from aqueous solutions. Besides, the heat treatment of some materials increases their affinity to copper ions. Thus, an equilibrium state between the clay particles and the copper ions is reached immediately after contact. Other studies on adsorption isotherms have shown that the efficiency of removal for copper ions follows two models, namely: Freundlich and Langmuir, which maintained that the process of bentonite absorbing copper ions is simply based on ionic exchanges. When the natural material (BN) activated is heated, its capacity to remove copper ions is increased, and also the Kd values are increased. This technique applied in clay materials could be the solution to the treatment of water often contaminated by heavy metals such as lead and copper. This study could lead to essential insights that would help in the treatment of industrial wastewater before it could be released to the ecosystem. Based on the effects of exposure to heavy metals on human beings and other living organisms, a solution should be sought fast enough to ensure that the water we consume is free of these toxic elements. Therefore, the discovery of an economical method of treating effluents would be essential, and this study can be considered as a step in the right direction.

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)