Chemical ReviewsREVIEW climatic conditions. Here, groundwater flow is slow and reaction times between water and rocks are therefore enhanced. Fluoride buildup is less pronounced in the humid tropics because of high rainfall inputs and their diluting effect on groundwater chemical composition. However, in tropical countries like India, the problem of excessive fluoride is more severe, particularly in arid parts of the country. Beside natural sources, fluoride ions can also be found in effluents from semiconductor, metal processing, fertilizers, and glass-manufacturing industries. 3À7 The discharge of such wastewater into the surface water would lead to increased levels of fluorides in surface and groundwater. Global and Indian Scenario1.2.1. International Status. The problem of excessive fluoride in drinking water has engulfed many parts of the world, and today many millions of people rely on groundwater with concentrations above the World Health Organization (WHO) guideline value. 8 There are >20 developed and developing nations in which fluorosis is endemic. 9 High fluoride concentrations in groundwater are also found in the USA, Africa, and Asia. 10,11 The most severe problem associated with high fluoride waters occurs in China, 12 India, 13 Sri Lanka, 14 and Rift Valley countries in Africa. High fluoride ground waters have been studied in detail in Africa, in particular in Kenya and Tanzania. 15À19 High fluoride groundwater is also found in the East Upper Region of Ghana. 20 In the early 1980s, it was estimated that ∼260 million people worldwide (in 30 countries) were drinking water with >1 mg/L of fluoride. 21 1.2.2. Current Status in India. In India, fluoride was first detected in drinking water at Nellore district of Andhra Pradesh in 1937. 9 Since then, considerable work has been done in different parts of India to explore the fluoride-laden water sources and their impacts on human as well on animal health. At present, it has been estimated that fluorosis is prevalent in 17 states of India, indicating that endemic fluorosis is one of the most alarming public health problem of the country, especially in Rajasthan,

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Zeolite 13X has been modified with monoethanol amine (MEA). MEA loadings of 0.5-25 wt % have been achieved using the impregnation method in different solvents. The mode of incorporation based on methanol with stirring at room temperature appears to be the most feasible. The adsorbent has been characterized for crystallinity, surface area, pore volume, and pore size. The thermal stability of the adsorbent is studied using a thermal analyzer. The CO 2 adsorption capacity of adsorbents is evaluated using the breakthrough adsorption method with a packed column on a 10 g scale. The adsorption capacities of adsorbents are estimated in the temperature range 30-120 °C. The adsorbents show improvement in CO 2 adsorption capacity over the unmodified zeolite by a factor of ca. 1.6 at 30 °C, whereas at 120 °C the efficiency improved by a factor of 3.5. For adsorption at these temperatures, different MEA loading levels were found to be suitable as per the governing adsorption phenomena, that is, physical or chemical. The adsorbent is also studied for CO 2 selectivity over N 2 at 75 °C. The MEA-modified adsorbent shows better CO 2 selectivity, which was improved further in the presence of moisture.

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The feasibility of using surfactant-modified zeolite (SMZ) as a carrier for fertilizer and for slow release of phosphorus (P) was investigated. Zeolite-A was modified by using hexadecyltrimethylammonium bromide, a cationic surfactant, to modify its surface to increase its capacity to retain anion, namely, phosphate (PO4(3-)). SMZ was thoroughly characterized using X-ray diffraction, Fourier transform infrared, and scanning electron microscopy to study the effect of surfactant modification. Zeolite-A and SMZ were then subjected to P loading by treating them with fertilizer (KH2PO4). It was observed that the P loading on SMZ increased by a factor of 4.9 as compared to the unmodified zeolite-A. A comparative study of the release of P from fertilizer-loaded unmodified zeolite-A and SMZ and from solid KH2PO4 was performed using the constant flow percolation reactor. The results show that the P supply from fertilizer-loaded SMZ was available even after 1080 h of continuous percolation, whereas P from KH2PO4 was exhausted within 264 h. The results indicate that SMZ is a good sorbent for PO4(3-), and a slow release of P was achievable. These properties suggest that SMZ has a great potential as the fertilizer carrier for slow release of P.