Investigating the efficiency of lemon peel waste as an adsorbent in the removal of cobalt, cadmium and nickel

Abstract

This research was conducted in order to investigate the absorption characteristics of cobalt, cadmium and nickel metals using lemon peel. The effect of different parameters such as pH of the solution, amount of adsorbent, contact time and temperature on the absorption process was investigated and the optimal operating conditions for the absorption of each element on the bio adsorbent were determined. The adsorption equilibrium values ??were investigated with Langmuir, Freundlich, Temkin and D-R isotherm models and the parameters of each model were determined. Among the adsorption isotherms, it was observed that the most appropriate isotherm model for this adsorption process is the Freundlich model. In this research, the maximum amount of absorption of cobalt, cadmium and nickel using the Langmuir model was 42.17, 23.07 and 23.05 mg/g, respectively. Different adsorption kinetics models were investigated for this process and pseudo-quadratic model was recognized as the best model. Also, the thermodynamic parameters of the absorption process by lemon peel such as Gibbs free energy, enthalpy changes and entropy changes were estimated at four different temperatures and the results showed that the absorption of cobalt, cadmium and nickel by lemon peel is a spontaneous and endothermic process. Also, the mechanism of the absorption process was determined using FTIR and SEM analyses.

Key words: biological absorption, cobalt, cadmium, nickel, lemon peel, isotherm, kinetics

Introduction

As we know, water is the most basic substance for life. It is on the planet. 97% of the water on earth is salt water, 2% is natural glaciers in the north and south poles, and only less than 1% of water on earth is fresh water, which is used for drinking, agriculture, domestic and industrial use. In recent decades, population growth and increased industrial activities have caused more and more complex environmental problems. (Kanz et al., 2002) [1] The rapid progress in industrial activities and the construction and establishment of factories as well as the development of technology has caused extensive and dangerous pollution in the human living environment and become a serious threat to human health. (Zheksian et al., 2006) [2] In fact, a significant amount of these pollutants are found in the atmosphere, soil, and water, and these activities collectively cause surface water, underground water, and sea pollution. With population growth, water consumption increases, but its supply is limited and this limited amount is also polluted by various pollutants. The main sources of water pollution are solid waste, radioactive waste, thermal pollution. (Tyagi and Mehra; 1994) [3] A number of domestic and industrial activities such as burning fossil fuels, burning waste, smelting processes, mining, battery industries, etc., cause the production of these pollutants, especially heavy metals. Today, minimizing the production of hazardous waste and heavy metals is one of the most important environmental challenges that the world is facing today. Heavy metals are dangerous non-degradable substances that can accumulate in elements of the human environment, including food, and endanger human health. (Kausarne and Yu, 2001; Yan and Viragavan 2001) [4] There are various methods for removing heavy metals, including chemical precipitation, membrane filtration, ion exchange, liquid extraction, and electrodialysis, etc. (Iqbal et al., 2002)[5] These methods are not used in large scale industries due to high cost. Currently, extensive industrial use of low-cost adsorbents is recommended due to their availability for wastewater treatment. (Al-Ashe et al., 2000; Bailey et al., 1999) [6]

There are different types of adsorbents for the absorption of heavy metals, the most suitable of which are agricultural waste and by-products. (Sari et al., 2008)[7]

The purpose of this project is to investigate the efficiency of lemon peel waste as an adsorbent in removing cobalt, cadmium, and nickel from aqueous solutions, and equilibrium and kinetic studies have been performed to describe the absorption process. Also, different models were tested to determine the rate and mechanism of the absorption process.

1-1 Heavy metals

Major environmental pollutants may include heavy metals and persistent organic pollutants such as chemicals, polychlorinated biphenyls, dioxins and furans. These wastes may be infectious, toxic or radioactive. (Anjur, 2007) [8] Three types of heavy metals of concern are: 1- Toxic metals (lead, copper, nickel, cobalt, cadmium, zinc, tin, etc.) 2- Precious metals (platinum, silver, gold, palladium, etc.) 3- Radioactive (thorium, etc.) (Wang and Chen, 2006) [9]

       Heavy ions of various toxic metals through metal industrial activities such as electroplating, mining, chloralkali, radiator production, metal melting, alloy industries, electrical and electronic industries, petrochemical, electrolysis, electroosmosis, etc. Or non-metallic industrial activities such as printing, photographic industries, oil refineries, paper, leather industries, sewage, fertilizers and pesticides, aerospace, nuclear power plants, etc. are formed and are one of the main causes of water pollution. (Khalafo and Menya, 2012) [10] The remaining heavy metal ions may accumulate in microorganisms, plants and animals, which in turn enter the human food chain and lead to many health problems. (Erzko, 2008) [11]

       Heavy metals cause serious environmental pollution and thus a threat to human health and the ecosystem. The presence of heavy metals in drinking water will have extensive adverse effects on the health of the human body, of which several examples can be mentioned. For example, these metals target the liver, kidneys, lungs and bone marrow. (Salem et al., 2000) [12] Skin lesions and cancer, allergies, high blood pressure, cardiovascular diseases, lung diseases (Smith et al., 2000) [13] Weakness, lethargy, damage to the digestive system, abdominal pain, muscle cramps, ailments, neurological diseases, behavioral changes, language and speech problems, and growth defects are among other problems caused by this problem. (Kapoor et al., 1999)[14]

For example, thorium is one of the radioactive elements that is widely distributed on the earth's crust. This radionuclide ion is toxic and dangerous and even in very small amounts it is very harmful to human physiology and other biological systems and can cause various diseases. Some human activities, including nuclear fuel processing and ore exploitation, can cause the release of this radionuclide. (Van Horn and Huang, 2006)[15]

      Among the heavy metals, lead is one of the most toxic, which enters the human body through cultivation in polluted soils, breathing air in industrial environments such as battery factories and drinking polluted water, and causes serious problems such as nausea, cancer, convulsions and degeneration of the central nervous system. (Lee et al., 2005)[16]

Arsenic is one of the other heavy metals found in drinking water. Nervous disorders, loss of appetite, bladder and kidney cancer, changes and thickening of the skin, muscle wasting are among the problems caused by this poison. (Jin and Ali, 2000)[17]

Below we describe 3 examples of heavy metals that were investigated in this research.

1-1-1 Cobalt

Cobalt is a hard ferromagnetic element with the chemical symbol Co which has a color It is shiny gray. Cobalt has a specific weight of 8.756 grams per cubic meter, melting point is equal to 1493 degrees Celsius, its electrical conductivity is about 16% of copper. This element is often associated with nickel and both of them are characteristic components of meteorite metal. Mammals require a very small amount of cobalt salts. Cobalt 60, which is a radioactive and synthetic isotope of cobalt, is an important source of gamma, a radioactive tracer and an agent of radiotherapy and cancer treatment. Of course, the ingestion of cobalt 60 leads to the entry of some cobalt into the tissues of the body, which is slowly removed from the body. The relative permeability of cobalt is two-thirds of that of iron. The normal oxidation states of cobalt include 2+ and 3+, although 1+ has also been observed. Cobalt has a relatively low abundance in the earth's crust and is deposited in natural waters as insoluble cobalt sulfine (COS).