Academic literature on the topic 'Adsorption cadmium ions'

In the adsorption of cations by soils, except for the electrostatic force discussed in Chapter 3, specific forces between the surface of soil particles and the cations may sometimes be involved. The adsorption caused by these specific forces is called specific adsorption. Apparently, this adsorption would be related to both the nature of the cations and the surface properties of the soil. Generally speaking, various oxides are the principal materials responsible for specific adsorption of cations in soils. Variable charge soils contain large amounts of iron and aluminum oxides. At the same time, their negative surface charge sites that can attract cations electrostatically are small in quantity. It can be expected that, compared to constant charge soils, their specific adsorption for cations would have more significance. Most of the cation species that can be adsorbed specifically by soils, such as copper, zinc, cobalt, and cadmium, belong to heavy metals. A large part of these heavy metals are transition elements in the periodic table. Alkali metal and alkaline earth metal ions can also be adsorbed specifically to some extent by soils under certain circumstances. However, this kind of adsorption is of less importance when compared to electrostatic adsorption, and the mechanism involved may be different from that for heavy metals. Among heavy metals, zinc occupies a special position in soil science because it is one important nutrient element for plants. In this chapter, after treatment on the principles of specific adsorption of heavy metal ions, detailed discussions will be presented for both the relative importance of specific adsorption and electrostatic adsorption of these ions and the consequences of specific adsorption, using the adsorption of zinc ions as an example. The cause of the difference in properties between the transition metal ions and the alkali metal and alkaline earth metal ions with respect to adsorption lies primarily in the difference in their atomic structure. Alkali metal and alkaline earth metal ions are characterized by a small amount of electric charge in the atomic nucleus, large ionic size, and weak polarizability. Therefore, the atom is difficult to deform.

The production of large quantities of agro/food wastes from food processing industries and the release of pollutants in the form of heavy metals from various metallurgical industries are the grave problems of the society as well as serious threats to the environment. It is estimated that approximately one–third of all food that is produced goes to waste, meaning thereby that nearly 1.3 billion tonnes of agro/food wastes are generated per year. This readily available and large amount waste can be utilized for the removal of toxic metals obtained from metallurgical industries by converting it into the adsorbents. For example, mango peel showed adsorption capacity of 68.92 mg/g in removing cadmium II ions. Similarly, coconut waste showed a higher adsorption capacity of 285 and 263 mg/g in removing cadmium and lead ion, respectively. Biosorption and bioaccumulation are recommended as novel, efficient, eco-friendly, and less costly alternative technologies over the conventional methods such as ion exchange, chemical precipitation, and membrane filtration, etc. for the removal of toxic metal ions. Because of the presence of metal-binding functional groups, the industrial by-products, agro-wastes and microbial biomass are considered as the potential biosorbents. Thus they can be used for the removal of toxic metal ions. This chapter highlights the available information and methods on utilizing the agro/food waste for the eradication of toxic and heavy metal ions. Furthermore, this chapter also focuses on the sorption mechanisms of different adsorbents as well as their adsorbing capacities.