The demand for the recovery of valuable metals and the need to understand the impact of heavy metals in the environment on human and aquatic life has led to the development of new methods for the extraction, recovery, and analysis of metal ions. With special emphasis on environmentally friendly approaches, efforts have been made to consider strategies that minimize the use of organic solvents, apply micromethodology, limit waste, reduce costs, are safe, and utilize benign or reusable materials. This review discusses recent developments in liquid- and solid-phase extraction techniques. Liquid-based methods include advances in the application of aqueous two- and three-phase systems, liquid membranes, and cloud point extraction. Recent progress in exploiting new sorbent materials for solid-phase extraction (SPE), solid-phase microextraction (SPME), and bulk extractions will also be discussed.

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The present study was focused to estimate six characteristics of soil specimens taken from 0.3 to 1.5 m sampling depth of six sampling sites of Budhanilkantha-Maharajganj roadsides using standard methods, and was assessed their corrosive nature to the buried-metallic pipelines using an empirical corrosion rating model. The estimated soil pH, moisture, resistivity, redox potential (ORP), chloride and sulfate ions were 6.4-7.9, 7-45%, 4.5 × 10 3 -45.5 × 10 3 Ohm. cm, 317-514 mV (SHE), 12-86 ppm, and 40-294 ppm, respectively, in all the soil sample specimens. The experimental results indicated that the soils could be rated as mildly corrosive to less corrosive groups to the buried galvanized-steel and cast iron pipes in the study areas. A good positive or negative correlation coefficient between resistivity, moisture, chloride and sulfate contents implies that these soil parameters have an equal contribution to the rating of soil corrosivity. A polyethylene-sheet wrapping (i.e., encasement) around the galvanized-steel and cast iron water pipelines or the use of non-conducting materials of gravel/sand around the burying ground could be sufficient for the extension of their life up to 50 years or more. The empirical model is successfully applied for the corrosion rating of soil samples and could be progressive in the future for soil corrosion rating of soils to the underground waterworks. Present findings would be insightful and suggestive in making the corrosive land maps of the studied areas which would be helpful for the potable water pipeline works in other urban areas of Nepal.