AB S TRAC T:Adsorption kinetic and equilibrium studies of two reactive dyes, namely, Reactive Red 31 and Reactive Red 2 were conducted. The equilibrium studies were conducted for various operational parameters such as initial dye concentration, pH, agitation speed, adsorbent dosage and temperature. The initial dye concentration was varied from 10 -60 mg/L, pH from 2 -11, agitation speed from 100-140 rpm, adsorbent dosage from 0.5 g to 2.5 g and temperature from 30 o C -50 o C respectively. The activated carbon of particle size 600 µm was developed from preliminary tannery sludge. The dye removal capacity of the two reactive red dyes decreased with increasing pH. The zero point charge for the sludge carbon was 9.0 and 7.0 for the two dyes, respectively. Batch kinetic data investigations on the removal of reactive dyes using tannery sludge activated carbon have been well described by the lagergren plots. It was suggested that the Pseudo second order adsorption mechanism was predominant for the sorption of the reactive dyes onto the tannery sludge based carbon. Thus, the adsorption phenomenon was suggested as a chemical process. The adsorption data fitted well with Langmuir model than the Freundlich model. The maximum adsorption capacity(q 0 ) from Langmuir isotherm were found to have increased in the range of 23.15-39.37 mg/g and 47.62-55.87 mg/g for reactive dyes reactive red 31 and reactive red 2, respectively.

The developed cationic tannery sludge carbon was found to be an effective adsorbent in the removal of the anionic azo reactive dye RR31.

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Calcium hydroxyapatite (Ca-HAp) was synthesized from calcium carbonate (CaCO3) extracted from a paper mill sludge. The extraction of CaCO3 was carried out by chemical precipitation process and synthesized to HAp nanoparticle under appropriate stoichiometric condition through wet chemical precipitation process. The size of the HAp nanoparticle was 42.5 nm under an optimized aging period of 24 h. This work aims in the batch adsorption of arsenic, an anionic metal arsenic in the form of Arsenite: As(III) on the synthesized Ca-HAp in laboratory scale. Batch kinetics studies were conducted for varying operational parameters such as temperature, initial adsorbate concentration, dye solution pH and rotation speed (RPM). In comparison with the two suggested isotherm models, Langmuir isotherm was suited to this adsorption process with a correlation coefficient of 0.92 and isotherm constant as 1.18 (KL). Chemisorption was found to be the rate-limiting mechanism for the sorption of arsenite onto Ca-HAp and thus followed pseudo-second-order kinetics. A maximum monolayer adsorption of 0.43 mg/g of arsenic was obtained at an equilibrium time of 60 min with 93% to 94.2% removal efficiency.