## 1 Introduction  
Nowadays, the production of water that contains heavy metals and chemicals is increasing due to rapid technological and industrial development. The primary producers of wastewater containing heavy metals are the leather, wool, cashmere, painting, mining, and metallurgy industries. Pollluted water that contains heavy metals, including chromium, lead, copper, mercury, and nickel, can create ecosystem imbalances and cause cancer [1; 2; 3]. Heavy metal pollution in the environment usually follows the following cyclic order: from manufactory to the atmosphere, soil, water, and food to living organisms. When heavy metals enter the human body through food or water, they are acidified in the stomach. In this acidic medium, metals are oxidized to their various oxidative states, which can readily bind to biological molecules such as proteins and enzymes to form stable and intense bonds and free radicals. These can damage biological molecules. Therefore, the treatment of wastewater is necessary to protect the environment and human health [4; 5]. Copper, one of these heavy metals, can cause brain and kidney damage in humans and living organisms. Researchers have applied the chemical precipitation, ion exchange, precipitation, adsorption, membrane separation, and reverse osmosis methods for wastewater treatment. In recent years, studies on the separation of heavy metals using supported liquid membranes material have attracted many researchers' interest [6; 7; 8]. Of these methods, the adsorption method is the most selective and efficient if the cost of the adsorbent can be reduced [4]. Adsorbents are classified as follows, depending on the base material from which they are developed. These include adsorbents based on carbon, chitosan, and mineral (zeolite); magnetic adsorbents; biosorbents; and metal-organic or synergistic adsorbents [7; 9; 10; 11; 12; 13; 14]. The hydrated silicate mineral is one of the most efficient, low-cost, and environmentally friendly absorbent materials, and it can be used as a material for wastewater treatment [2]. Mesoporous aluminosilicates exist naturally and can be extracted synthetically. Zeolites are useful as catalysts for synthesis and in the polymerization of semiconducting materials and conducting polymers. The high surface area and pores of zeolites give zeolites unique adsorption properties. Zeolites have a large surface area due to their excellent porosity. The three-dimensional framework of SiO\({}_{4}\) and AlO\({}_{4}\) tetrahedra in the structure of zeolites is ordered and contains pores and spaces. Based on natural zeolite characteristics, composite materials with a high removal efficiency of organic, cationic, and anionic pollutants from wastewater have been created [10; 15; 16]. Mongolia has several deposits of natural zeolite reserves. The Tsagaantsav is one of the largest zeolite deposits in Mongolia, with 4.8 million tons of zeolite minerals, located 540 km from the capital city of Mongolia, Ulaanbaatar. Researchers have conducted several studies on the adsorption of heavy metals by using Mongolian zeolite due to its characteristics, such as its porosity, ion-exchange capacity, and reusability [17; 18; 19]. For example, researchers investigated the adsorptions of heavy metals from model aqueous wastewater by Tsagaantsav natural zeolite and have concluded that the cation-exchange capacity of the raw zeolite sample is proportionally related to the aluminum content [19]. Researchers studied the structural characterization and adsorption capacities of Pb\({}^{2+}\), Cd\({}^{2+}\), and Zn\({}^{2+}\) on the Tsagaantsav deposit and determined that the Tsagaantsav zeolites are highly effective at adsorbing Pb\({}^{2+}\) under acidic conditions, compared with Cd\({}^{2+}\) and Zn\({}^{2+}\) cations [20]. However, the practical application usage of natural zeolite is limited by its lower adsorption capacity and selectivity.