Adsorption at Natural Minerals/Water Interfaces

Removal of heavy metals from aqueous solutions has gotten considerable attention over the years by using adsorbents derived from low-cost materials, especially natural minerals. Treating the pollution of wastewater with the natural minerals, has advantages of wide sources of materials, cheap price, low energy consumption, the higher removal efficiency. This chapter introduces the latest research on the natural mineral adsorbents including montmorillonite, kaolinite, sepiolite, diatomite, vermiculite, perlite, zeolite, etc., which are classified as layered minerals, porous minerals and others according to the structural characteristics. The mineralogical characteristics of the mineral adsorbents including pore structure, specific surface area, morphology and ion-exchange property are presented and the effect of the mineral structure on the adsorption performance of the mineral adsorbents is discussed. The surface characterization technologies for determining surface chemical component, surface charge, surface areas, surface morphology and surface interaction are also presented.

Surface chemistry of mineral adsorbents dominates the interaction of adsorbent and adsorbates, and thus the adsorption. The surface chemistry related to adsorption at solid/liquid interfaces including surface areas, surface charges, surface interactions, adsorption thermodynamics and kinetics, etc. are described in the chapter. The roles of surface area, surface charge, and surface interaction in the adsorption of contaminants have been deep discussed. In addition, the chapter also reviewed the characterization technology of adsorption including component, structural and morphology, surface and interface properties, and other properties. The chapter provides a fundamental understanding of the surface chemistry of mineral adsorbents for the selection, development of efficient mineral based adsorbents.

The modification of mineral surfaces and microstructures is generally an effective method to change and/or tailor the adsorption performance of mineral adsorbents. In this chapter, the aims, principle processes and mechanisms of the modification methods, including adsorption, intercalation, acid modification, thermal modification, grafting and coating, etching, etc., are summarized in detail. The characteristics of common modifying agents and their applications in the surface modification are also introduced. Finally, the commonly used measurements and/or evaluation methods for the surface modification of materials are listed.

Natural minerals stand out from conventional materials as promising adsorbents for the anions removal from aqueous solution due to their efficient adsorption performance, cost-effectiveness and easy-availability. This chapter summarizes the advances of natural minerals as adsorbents for the removal of anions (arsenic, phosphorus, fluoride, nitrate) in water. The common natural minerals, as well as their adsorption capacity, are introduced for each anion. The affecting factors and adsorption mechanism are also highlighted.

The adsorption of cations on minerals plays an important role theoretically in surface and colloidal chemistry, and applicably in various engineering processes such as water treatment, agriculture and flotation of minerals. This chapter introduces the fundamentals of the adsorption of cations on minerals, the measurements, and classifies the applications. Then, structure and surface chemistry of clay minerals, which have been proved to be the most workable mineral in cations adsorption, are introduced. Other oxide minerals, such as goethite, are present for their structure and adsorption behavior as well. After that, the chapter summarizes and differentiates the adsorption on the basis of different types of cations, namely lead, mercury, copper, chromium and other cations. It tries to present the research results through a novel classification, rather than the types of adsorbents. The gaps between fundamental research and engineering applications are discussed, as well as the further research opportunities are present.

Organic compounds have attracted extensive concerns in water treatment, agriculture and ecological engineering due to most of which are poorly-biodegradable and highly-toxic to aquatic ecosystem as well as the human beings. Therefore, developing efficient and economical technologies to remove organic contaminants from aqueous system is highly essential for ensuring the safty of drinking water for human beings. In this chapter, the adsorption of organic compounds on minerals, which is one of the most promising technologies for removing organic compounds, will be discussed. Four kinds of typical organic compounds, i.e. dyes, phenolic compounds, antibiotics and perfluorooctane sulphonate were discussed in detail. The physical and chemical properties of each organic compounds were firstly introduced. Then the structure and properties of minerals which were appropriate to immobilize organic compounds were reviewed. In the meanwhile, in each section, the adsorption process of those organic compounds on minerals and the related adsorption mechanism were also discussed. This chapter provided a comprehensive insight into the role of natural or modified minerals in organic compounds adsorption, which probably pave the way for organic wastewater treatment.

Adsorption of microorganisms (bacteria, fungi and microalgae, etc.) and biomacromolecules (humic substances, extracellular substances, proteins and nuclear acids, etc.) to minerals are universal in the nature environments. These processes also governed the inorganic and organic pollutants migration and conversion. This chapter discusses the interface reactions of microorganisms and minerals regarding the surface properties of both sides, leading to the microorganism’s survival and growing, minerals’ transformation and formation as well as polluted or harmful substances’ retention and removal. The content broads the knowledge of bacteria, fungi and algae and biomacromolecules adsorption onto natural minerals and highlights the application of microorganism-mineral interaction on environmental engineering such as heavy metals and polluted organic matters removal.

This chapter will comprehensively introduce the most common water types (free water, vicinal water, bound water, interstitial water, etc.) adsorbed by various mineral adsorbents such as montmorillonite. In addition, the most usually used dewatering strategies and the processes including thickening, filtration, centrifugation, incineration that can be applied to efficiently separate the liquid from the solid minerals will be demonstrated, achieving a low moisture content to meet the disposal or reuse purposes. Moreover, the dehydration mechanisms for each water type will also be illustrated. Finally, the most recently developed dewatering methods for other solid-liquid separation will also be introduced and explained as the promising potential means in dewatering mineral adsorbents.