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Adsorption processes are extensively used in wastewater treatment for heavy metal removal. The most widely used adsorbent is activated carbon giving the best of results but it’s high cost limits its use. It has a high cost of production and regeneration. As the world today faces a shortage of freshwater resources, it is inevitable to look for alternatives that lessen the burden on existing resources. Also, heavy metals are toxic even in trace concentrations, so an environmentally safe method of their removal necessitated the requirement of low cost adsorbents. Adsorption is a cost-effective technique and gained recognition due to its minimum waste disposal advantage. This chapter focuses on the process of adsorption and the types of adsorbent available today. It also encompasses the low-cost adsorbents ranging from agricultural waste to industrial waste explaining the adsorption reaction condition. The cost-effectiveness, technical applicability and easy availability of raw material with low negative impact on the system are the precursors in selecting the adsorbents. The novelty of the chapter lies in covering a wide range of adsorbents with their efficiency in removal of heavy metals from wastewater.

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Second-order rate constants (k 2 ) of the reaction between phenacyl bromide and equimolar mixture of nitrobenzoic acid(s)-triethylamine have been determined in dimethylformamide (DMF)/acetonitrile (ACN)/acetone and aqueous mixtures of these solvents by conductometric method at 30 • C. The rates of nitrobenzoic acids are found to be in the order: 4-NO 2 > 3-NO 2 > 3,5-(NO 2 ) 2 . Changes in the rate just by the addition of water (1% (v/v)) into organic component is rationalized. Decrease in the values of k 2 on increasing water content in organic solvent is explained on the basis of preferential solvation phenomenon. Single and dual regression analysis using the various solvent parameters of aqueous mixtures (E T (30), Z, π * , β, α, and Y) resulted in π * and α as the best parameters to explain solvation of nitrobenzoates. C