The Extraction of Copper Ions From a Solution Using Coffee Grounds

Abstract

Heavy metal contamination of bodies of water can the stunt growth and development of a range of flora, as well as negatively shift the environment and affect fauna. Current methods of metal extraction through adsorption are costly, initiating research into cheaper, more environmentally friendly alternatives. One such avenue is the use of bio-adsorbents: a cost-efficient, naturally occurring, and waste-minimizing collection of compounds effective in removing heavy metals from a solution.

This study analyzed the use of coffee grounds as an effective bio-adsorbent in removing copper (Cu(II)) ions from a solution. Furthermore, research was carried out across a range of temperatures to test if the percentage removed was affected. Results elucidated the percentage of Cu(II) ions removed from a solution increased at a dampening trend, as the temperature of the solution increased. The percentage of Cu(II) ions was most effective at 50ᵒC with treatments differing greatly at cooler temperatures of 10ᵒC and 22ᵒC (room temperature).

This data highlights that coffee grounds are an effective bio-adsorbent in treating bodies of water contaminated by heavy metals such as Cu(II). Furthermore, this study proves coffee grounds are increasingly effective under higher temperatures.

Introduction

Water is a crucial component towards survival in both flora and fauna, generating approximately 60% of body mass in most mammals alone. This natural reliance highlights the critical issue of metal contamination in bodies of water. Agricultural and mining practices, such as algae control and acidic mining, are the largest contributors to water contamination due to these processes' leeching large quantities of heavy metals into waterways. Corporations operating rurally pose an increasing impact on surrounding foliage. Results deduced from several studies in Europe, Canada, and the USA, by the World Health Organisation, highlighted that copper levels in drinking water can range from 0.005mg/liter to 30 mg/liter. These findings suggested that these levels were a cause of corrosion of interior copper plumbing.

Heavy metal contamination can lead to severe health effects including vomiting, diarrhea, and stomach cramps, and further develop into liver damage and kidney disease. Foliage bordering Cu(II) contaminated waterways or present in the vicinity of factories reliant on heavy mental processes, can exhibit restricted root growth, as well as compete for more critical mineral intake such as Iron Fe(II)/Fe(III) or Zinc Zn(II).

Current methods of Cu(II) extraction such as Membrane Filtration, Cementation, and Electrodialysis require high maintenance, excess power, and can pose a safety hazard, limiting their integration into economically strained countries. Numerous studies assessed the adsorption of the heavy metal ions Cu2+, Zn2+, Cd2+, and Pb2+ from aqueous solutions by using coffee grounds.

Natural bioadsorbents have been investigated as a potential low-cost treatment method for heavy metal-containing wastewater as they are readily available natural by-products. Current uses of bioadsorbents such as COCB (chitosan–oxalate complex biosorbent) and Activated Carbon exhibited fast adsorption rate and high adsorption capacities for Cu(II) uptake.

In this study, it was aimed to enhance the claims of coffee grounds as an effective natural bio-adsorbent and further test the effect of adsorption under a range of solution temperatures.

Methodology

This study was conducted in two parts.

A) The construction of a calibration curve.

B) The effect of temperature.

Calibration Curve

To assess the adsorption capability of Coffee Grounds, a calibration curve was created. A calibration curve is the standard method for calculating the concentration of a substance in an unknown sample by estimation against samples of known concentration.

10mL of 0.5, 1, 2,5, and 10 copper solutions were dispensed into five vials, with a sixth vial filled with 10mL of water to act as a blank recording. 5mL of Ammonium acetate buffer and 5mL of Alizarin Red were added into each sample and vortexed. The samples had their concentrations measured, and with these measurements, the curve was generated.

Effect of Temperature

To determine the effect of different temperatures on the adsorption of copper, 0.1g of coffee grounds was measured out into four vials. 10mL of 5ppm copper solution was added into each vial. The samples were vortexed for 10 seconds and left to rest for 10 minutes. After 5 minutes in the centrifuge, the samples were removed and 2.5mL of alizarin red was added to each sample.

As this experiment covered a range of temperatures, one sample was cooled to 10°C, another remained at room temperature, and the remaining two were heated to 30°C and 50 °C, respectively. Following this, the absorbance was recorded.

Results

As the average concentrations of Copper in the solution increased, so too did the absorbance. The blank, 0.5, and 1 ppm concentrations highlighted average absorbances of 0.237, 0.258, and 0.259, respectively. At 2ppm, the absorbance didn’t reach double 1ppm at 0.343 with the following results not following in suit (5ppm 0.513, 10ppm 0.726). This calibration curve is highly accurate regardless as the R2 value, which measures the ‘straightness’ of a line, is close to 1 at 0.9963 as shown in Figure 1.1.Figure 1.1: The calibration curve is a large, linear, positive association.

Effect of Temperature

The percentage of Cu(II) ions removed from a solution increased as the temperature increased. This was recorded highest at around 50°C at an average of 51%. As is evident in Figure 1.2, this percentage slowly decreased in a non-linear pattern to 49% at 30°C and 48% at 22°C (room temperature). Most noticeably, the lower temperature highlighted a dramatic decrease in the percentage of Cu(II) ions removed to 37% at 10°C.

Discussion

The study of analyzing the extraction of heavy metals from bodies of water aimed to support emerging evidence of natural products as effective bioadsorbents. More specifically, this study tested the effectiveness of coffee grounds as a sustainable, cost-efficient product, in removing Cu(II) ions from a solution. Furthermore, it was aimed to assess whether the efficiency of using Coffee Grounds was determined by a specific temperature. The results elucidate that as the temperature increases, the percentage of Cu(II) ions removed from a solution also increases in parallel. The results also highlight that a decrease in temperature reduces the percentage removed. At 10°C, the adsorption percentage of Cu(II) ions was approximate ¾ the percentage of Cu(II) ions removed at room temperature (22°C).

Numerous studies support the claim that not only is coffee ground an effective bioadsorpent, but the percentage of metal ions removed from a solution is largely determined by temperature. This enhances the possibility of coffee grounds being used to remove Cu(II) ions from bodies of water. In a similar, combined study across numerous Taiwanese universities, Chou et al analyzed the effectiveness of spent coffee grounds in removing Indium ions (In(III)) from a solution. Indium, a heavy metal evenly distributed in the earth’s crust, shares similar qualities to Copper.

The results highlighted a significant increase in the percentage of Indium ion adsorbed as the temperature of the solution increased. At 308K (approx 35°C), the percentage of In(III) adsorbed was almost double the Cu(II) adsorbed at a similar temperature. At 288K (approx. 15°C), this was recorded at 61% Indium removed compared to 36% Copper removed. This inconsistency may have been due to the strength of intermolecular forces between Indium, Copper, and the Coffee Grounds. The mobility of indium ions, which increases generally with increasing temperature, may have resulted in the number of molecules able to gain enough energy to interact with active sites at the solid-liquid surface. This could have led to an increased adsorption efficiency compared to Copper when the temperature increases. Figure 2.1: The effect of temperature on the removal of In(III) ions using coffee grounds was recorded in mg/g.

A second study, presented to the ‘2017 International Conference of Alternative Energy’ looked at the adsorption of methyl orange through the conversion of coffee grounds into activated carbon, and then tested this effectiveness under varying temperatures. In this study, researchers found that by activating Coffee Grounds with Nitric acid and blasting the compound with heat to turn it into activated carbon, the coffee grounds became an effective adsorbent. However, results highlighted decreasing effectiveness of removal of coffee grounds above 30°C. This is completely opposite to the results gained. One response to this study highlighted that although a temperature increase results in the favorable intermolecular forces between adsorbate and adsorbent becoming much stronger than those between adsorbate and solvent (Alshamsi, 2017), the active site upon the Coffee Grounds may have reached a saturation point. Even though the temperature increase caused metallic bonds between copper ions to be outweighed by the electrostatic van de Waal attractions between copper ions and coffee grounds, the active site simply reached capacity and could not adsorb any further. Figure 2.3: The effect of temperature on the removal of Cu(II) ions using coffee grounds as activated carbon was recorded as mg/g.

There were numerous factors in this experiment which may have influenced the accuracy, reliability, and validity of the results. An ice bath was used to cool the solution to 10°C. Using a more natural means of cooling as opposed to an apparatus such as a fridge may have resulted in inaccurate temperature readings. Furthermore, the time between heating the copper solutions, then transferring the vessel to measure the absorbance, could have caused heat to be expelled into the environment. This loss of heat and the subsequent system realignment with room temperature could have led to a misinterpretation of results above room temperature.

Future research could record the pH of each solution to eliminate any doubt in the results. This is because the pH of water is known to affect the adsorption of a solution, which largely differs between neutral and acidic solutions. From a changing pH of 3 to a pH of 5, Cu(II) ion adsorption increased to 76% from 60% and thereafter remained almost constant for higher pHs.

While there are numerous studies analyzing the effectiveness of natural products as bioadsorbents, such as coffee grounds, there are few studies which accurately focus on the correlation between solution temperature and adsorption effectiveness. Similar studies analyzed the effectiveness of removal on other heavy metals, such as In(III) Chou et al., highlighting that coffee grounds removed a higher percentage of heavy metals as the temperature increased. Rather than analyze In(III) ions, this study specifically found that Coffee Grounds are increasingly effective in removing Cu(II) ions from a solution at higher temperatures.

Conclusion

Coffee grounds are an effective bio-adsorbent for the removal of Cu(II) ions from heavy metal polluted solutions. Furthermore, the effectiveness of Cu(II) ion removal increased as the temperature of the solution increased. As a cheap, natural, and sustainable by-product, coffee grounds can be a more appealing alternative towards decontaminating polluted waterways. These factors alone see coffee grounds making a more viable impact on economically strained countries, reducing health risks, and providing populations with access to cleaner, safer water.

Although studies have analyzed the effectiveness of coffee grounds on the removal of Cu(II) and In(III) ions under a shifting temperature, future research into other heavy metals is required in order to assess the versatility of Coffee grounds across waterways contaminated with multiple heavy metals. These include Chromium(III), Lead(II), and Nickle(II) ions.

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