Potential Heavy Metal Chemisorptive from Agro-processing Waste and Safe Dumping of Used Adsorbents

Daiana Cristóbal^*
*Correspondence: Daiana Cristóbal, Department of Chemistry, Faculty of Science, Edifici C-Nord, Universitat Autònoma de Barcelona, Carrer dels Tillers, 08193 Bellaterra, Spain, Email:

Keywords

Heavy metals • Agro-industrial waste • Adsorption • Wastewater treatment • Contaminant immobilization

Introduction

Water contamination is a major global environmental issue that is mostly brought on by climatic change, fast urbanisation, and industrialisation. Heavy metals are among the most frequently released pollutants or contaminants into the water and are not biodegradable; as a result, they build up in living things and enter the food chain, as well as through consumption of contaminated foods and water, resulting in corresponding pollution biomagnification. These metals pose a risk to the environment and public health not only because of their tenacity and concentration, which affect exposure, but also because of their toxicity and mobility in the environment, which determines their bioavailability. The type of compound or metabolite that each metal can form, as well as the characteristics of each individual environment, determine this bioavailability Common and important heavy metals in the environment are nickel, zinc, and cadmium [1].

The nickel, zinc, and cadmium contamination comes from a variety of human-made sources, including the electroplating, metallurgical, and battery sectors. Furthermore, due to mineral weathering, nickel and zinc can easily leach. Both Ni(II) and Zn(II) are essential elements that, in small amounts, are required for the metabolic growth of people, plants, and other creatures. However, when exposure or assimilation surpasses the upper limit of the physiologically needed range, these elements can be toxic and have detrimental effects on health. For instance, high nickel exposure can result in cancer, dry cough, lung issues, dermatitis, nausea, gastrointestinal issues, and renal difficulties in people, while high zinc exposure can result in fever, vomiting, anaemia, and skin issues in people [2].

Subjective Heading

Biomass characterization

Adsorbents' physicochemical characteristics play a role in the adsorption of pollutants. Numerous methods were used to determine the characteristics of potential adsorbents. These methods included the Brunauer-Emmett-Teller (BET) (Micromeritics Accusorb, model 2100), scanning electron microscopy (SEM) (ZEISS EVO® MA 10 at the UAB Microscopy Service and FEI ESEM Quanta 200), energydispersive X-ray spectroscopy (EDS) (Oxford SDD X- heating, air 10 °C/min to 1000 °C rate and about 20 mg of mass). The ASTM E1755- 01 standard's standards were used to estimate the mineral content of biomass. Additionally, the potential alterations in the biomasses brought about by the adsorption experiments were examined [3].

Batch adsorption experiments

At room temperature, batch adsorption studies were used to remove heavy metals using the agro-industrial residues stated above. A mono-metal solution of Ni(II), Zn(II), or Cd(II) in a volume of 10 mL with a concentration of 0.18 mmol/L or a multi-metal solution containing all three heavy metals with a concentration of 0.18 mmol/L each were placed in contact with 0.1 g of adsorbent in tubes. Following earlier studies, the pH of the solutions was originally adjusted to be between 4-5. To make sure equilibrium was established, the system was agitated for 24 hours at 40 rpm in a rotary mixer (CE 2000 ABT- 4, SBS Instruments SA). Through 0.22 m filters, the liquid phase was filtered (Millex-GS, Millipore, Burlington, MA, USA). The amount of metal in The Autonomous University of Barcelona used inductively coupled plasma-mass spectrometry (ICP-MS) (XSERIES 2 ICPMS, Thermo Scientific, Waltham, MA, USA) to identify the aqueous solution (not adsorbed).

Discussion

In comparison to Zn(II) and Cd(II), Ni(II) had a lower adsorption in all of the biomasses investigated, as indicated by the findings of the adsorption percentage (A%) and adsorption capacity (qe) obtained. For sawdust, sunflower, and corn, the adsorption proceeds as follows: Ni(II) Zn(II) Cd(II), as illustrated in Figure 9, as it was also observed for other waste of lignocellulosic origin, such as coffee dregs, rice husks, cocoa husks, and waste from paper manufacture. The various traits and affinities of the metal ions for adsorbent adsorption sites are related to this behaviour. The nickel ion has a larger hydration energy than the zinc and cadmium ions when comparing the values of the hydration energies (Ni(II): 2106 kJ/mol, Zn(II): 2044 kJ/mol, and Cd(II): 1806 kJ/mol), which are connected to the hydrolysis of metal ions [4].

It is harder to shed water molecules from its coordination sphere when there are ions present, which makes it more resistant to being adsorbed by the adsorbent through complexation or ion-exchange processes. Smaller ions are more hydrated than bigger ones, which may prevent adsorption, claim Mahmood-ul-Hassan et al. Higher pore volume, surface area, and mineral content in corn residues may have helped in the adsorption of heavy metals. However, there aren't many distinctions between the three biomasses in terms of the adsorption findings. The particle size of the sample, according to Mohajeran et al, regulates the contact surface with the leaching solution and consequently affects the concentration of heavy metals observed. Since clay bricks will typically be utilised whole rather than crushed in leaching tests, the leaching may actually be reduced even if there is now no regulation that requires a test or sets restrictions on the leaching of heavy metals in building materials [5].

Conclusion

The reductions of trash produced by agro-industrial activities and/or the reuse of this waste in products that enhance quality of life are current problems. In this regard, adsorption from agroindustry wastes is developing as a straightforward, inexpensive, and effective alternative to the current lack of a universal method to remove heavy metals from wastewater and effluents. Additionally, a solution for the secure disposal of such biomass adsorbents (including heavy metals as pollutants) following the adsorption process was put forth in this research effort. As an alternative to immobilising Ni(II), Zn(II), Cd(II), and their mixture, the stability of these used adsorbents in clay ceramics with potential application in construction is shown. The ceramic matrices made with additional wasted adsorbents confirmed an efficient immobilisation for all heavy metals, whose concentrations were found to be below the allowable levels, in heavy metal leaching experiments. Retention efficiencies of the clay ceramics exceeded 88.5%.

Acknowledgement

None.

Conflict of Interest

None.

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