The palygorskite-sepiolite group of clay minerals has a wide range of industrial applications derived mainly from its sorptive, rheological and catalytic properties which are based on the fabric, surface area, porosity, crystal morphology, structure and composition of these minerals. For assessing potential industrial uses, the mineralogical and chemical composition of the clay and its basic physical and physico-chemical parameters must be determined. Then some particular properties of commercial interest can be modified and improved by appropriate thermal, mechanical and acid treatments, surface active agents, organo-mineral derivatives formation, etc. In this paper, a revision of the principal characteristics of commercial palygorskite-sepiolite clays is presented, and potential uses are suggested according to these data. New products and applications are being investigated and those concerning environmental protection in particular, are noted. Finally, possible health effects of these elongate clay minerals are discussed. While commercial deposits of palygorskite and sepiolite are rare, these two clay minerals occur relatively frequently in sediments and soils. Both palygorskite and sepiolite clays are so- called 'special clays'. The annual production in the western world for the former is estimated to be around two million tonnes; production comes mainly from the southeastern USA (Miocene deposits in Florida and Georgia), about 1.8 million tonnes in 1989 (Ampian, 1991), and from Senegal, Spain, Australia, India, Turkey, South Africa and France to a much smaller extent. Sepiolite is less abundant than palygors- kite. The former is a typically Spanish mineral; in fact, over 90% of sepiolitic clays are produced in Spain (also from Miocene deposits). Other small operations are in Nevada (USA), Turkey and China. The annual production of sepiolite in Spain is close to 800,000 tonnes (O'Driscoll,

Properties and applications of palygorskite-sepiolite clays

Fibrous clays based bionanocomposites

Publisher Summary This chapter describes the beneficial and harmful effects of clay mineral. Clay minerals can be beneficial to human health by serving as active principles or excipients in pharmaceutical preparations, in spas, and in beauty therapy medicine. In some cases, however, these minerals may be harmful to human health. In pharmaceutical formulations, spas and beauty therapy, clay minerals are used for therapeutic purposes and their beneficial effect on human health. In pharmaceutical formulations, these minerals are used as active principles (gastrointestinal protectors, antacids antidiarrhoeaics, dermatological protectors, cosmetics) and excipients (inert bases, delivery systems, lubricants, emulsifiers). In spas and beauty therapy, clay minerals are used in geotherapy, pelotherapy, and paramuds to treat dermatological diseases, alleviate the pain of chronic rheumatic inflammations, moisturize the skin, and combat compact lipodystrophies and cellulite. However, clay minerals can also have an adverse effect on human health when they are inhaled over a very long period. In the lung, clay minerals can cause diverse pathologies such as cancer, mesothelioma, or pneumoconiosis, but the toxicity of these minerals is generally related to the presence of quartz or asbestos from mining operations. The pathogenicity of fibrous clay minerals (sepiolite and palygorskite) is related to the geological conditions of formation.

Chapter 11.5 Clays and Human Health

Bentonite, kaolin, and selected clay minerals

In this chapter, the beneficial and harmful effect of clays and clay minerals is described. Clays and clay minerals can be beneficial to human health by serving in pharmaceutical (as active ingredients and excipients) and cosmetic products (creams, powders and emulsions), in spas and beauty therapy (in pelotherapy to treat dermatological diseases, alleviate the pain of chronic rheumatic inflammations, moisturize the skin, and combat compact lipodystrophies and cellulite), or in other medical applications as diagnosis techniques. On the other hand, the toxicity of clay minerals is reviewed. Clay minerals can have an adverse effect on human health when they are inhaled over a very long period. Inside the lung, clay minerals can cause diverse pathologies such as cancer, mesothelioma, or pneumoconiosis, but the toxicity of these minerals is generally related to both the presence of quartz or asbestos from mining works, or with the geological conditions of formation.

Clays, Drugs, and Human Health

In vitro studies of the destruction (lysis) of bovine red blood cells (erythrocytes) by some silicate minerals showed the reaction to be complete in less than 1 hr and very destructive to the cell membrane. The activity as lysing agents was found to be in the order smectites > silica > palygorskite -~ sepiolite > chrysotile > kaolinite. Different compositions (Fe, A1, Mg, Li, vacancy) of the octahedral sheet of the smectite and fibrous clay minerals did not appreciably alter their hemolytic activity. The most active particle size range for kaolinite and montmoriUonite was 0.2-2 ~m. Structural folding of palygorskite reduced lysis suggesting that edge surfaces and silanol groups are important in this process. Aluminum oxides and hydroxides caused no lysis, and coatings of positively charged aluminum-hydroxy polymers on montmorillonite, silica, palygorskite, and kaolinite significantly reduced lysis.

D. W. Oscarson

Papers

Lysis of erythrocytes by silicate minerals