D. C. Rupainwar

Adsorption technique for the treatment of As(V)-rich effluents

Unconventional adsorbents like hematite and feldspar have been employed for the removal of AS(V) from aqueous system. The effect of important parameters like solute concentration, detention time, pH, temperature, agitation rate and particle size of the adsorbent has been addressed. The process of uptake follows first-order kinetics and the data fit the Langmuir isotherm. Mass-transfer coefficients and diffusion coefficients have also been determined to study the dynamics of transport. The pH of the system has been found to play a key role in the uptake. The maximum removal was found to be 100% with hematite and 97% with feldspar under optimum conditions at 13.35 μmol L−1 arsenic concentration. The data were subjected to multiple-regression analysis and a model has been developed to predict the uptake capacity of the adsorbents under given boundary conditions.

As(III) removal from aqueous solution by adsorption

The removal of As(III) from aqueous solutions at different concentrations, pH and temperatures by haematite has been carried out successfully. The maximum removal was found to be 96 % at concentration 13.34 μmol L−1, temperature 20 °C and pH 7.0. The process of uptake follows first-order adsorption rate expression and obeys the Langmuirs model of adsorption. The removal of As(III) by haematite is also partially diffusion controlled and mass transfer coefficients, diffusion coefficients and thermodynamic parameters have been determined to explain the results.

Studies on the Cd(II) removal from water by adsorption

The feasibility of using hematite for the removal of Cd(II) from aqueous solutions was investigated employing an adsorption technique. The adsorption was found to depend on Cd(II) concentration, pH, particle size of hematite, agitation rate and temperature of the system. The maximum removal was found to be 98% for the cadmium concentration of 44.88 μmol l−1 at a temperature of 20°C and pH 9.2 with 40 g l−1 of hematite of particle size <200 μm with agitation 125 rpm rate after 2 h. The applicability of the Langmuir isotherm was tested for the Cd(II)-hematite system at optimum conditions. The process follows first order kinetics. The mass transfer coefficient, diffusion coefficient and thermodynamic parameters have been determined to elucidate the mechanism of uptake. The uptake of cadmium is partially diffusion controlled and partially due to an electrostatic effect along with specific adsorption involving Cd++ and CdOH+ which seem to play an effective role. The data has been subjected to multiple regression analysis and a computer model has been developed to predict the removal of Cd(II) from water under certain boundary conditions. The present technique has been found to be cost-effective.

Use of wollastonite in the removal of Ni(II) from aqueous solutions

The ability of wollastonite to adsorb Ni (II) from water has been carried out. A removal of 92% of Ni (II) with 20 g L−1 of adsorbent was observed at 50 mg L−1 adsorbate concentration, 6.5 pH and 30 °C. The process follows a first order rate kinetics with diffusion controlled nature and the data fits the Langmuir adsorption isotherm. Removal of Ni increases from 10 to 92% with the rise of pH from 3.0 to 8.0 and thereafter it remains almost unchanged. This change has been explained on the basis of aqueous-complex formation and the subsequent acid base dissociation at the solid-solution interface.

Removal of ni(II) from aqueous solutions by sorption

Adsorption of Ni(II) from its aqueous solutions on China clay, a cheap clay mineral, has been found quite favourable; a maximum removal of 75.3% was obtained at 50 mg L‐1 metal concentration and a pH of 6.5 at 30°C. Dynamic modelling of the nickel uptake has been worked out and found to be of the first order. The rate constant was found to be 9.21 x 10‐1 min‐1 under the above optimum conditions of the experiment. Coefficients of the mass transfer and intraparticle diffusion were also evaluated and found to be 2.8 x 10‐2 cm s‐1 and 4.50 x 10‐2 cm2 s‐1 respectively. Langmuirs model was used for the equilibrium modelling and the constants were calculated at 30, 40 and 50°C. Thermodynamic study at different temperatures was undertaken and the values of change in the standard free energy (?G°), enthalpy (?H°) and entropy (?S°) are reported. Low temperature and high pH favour the removal of nickel (II) by adsorption on China clay.

Heavy metal pollution of river Ganga in Mirzapur, India

A study on the heavy metal pollution of River Ganga in the Mirzapur region, India has revealed that the river is polluted. The samples were collected from both the confluence of sewers and the river and from midstream points. The river is the dumping ground for domestic, municipal and industrial effluents. All the samples were analysed for certain physiochemical parameters i.e. temperature, pH, chloride content, alkalinity, dissolved oxygen and chemical oxygen demand. On analysis, the concentrations of most of the heavy metal ions were found to be above the prescribed limits for potable waters in the samples collected from confluence points. Cadmium and cobalt were in the range 13.37–32.73 μg/L and 10.50–26.77 μg/L respectively. Copper, iron and manganese were found in the range of 38.0–157.80 μg/L, 19.75–72.77 /ug/L and 34.25–105.55 yug/L respectively. Nickel was recorded to be in the range 67.25–176.13 mg/L while lead and zinc were in the range of 34.25–185.75 μg/L and 94.25–423.75 μg/L. Concentrations ...

The Use of Hematite for Chromium(VI) Removal

Abstract The ability of hematite to remove Cr(VI) from aqueous solutions has been studied at different concentrations, temperatures and pH. The maximum removal (97%) was observed at 40 °C and pH 2.7 with initial concentrations of 19.23 μmol/L Cr(VI) and 40 g/L hematite. The equilibrium data obey the Langmuir isotherm for the present system. The reaction dynamics have been studied and the process involves both film and pore diffusion to different extents. Mass transfer and diffusion coefficients have been determined. Thermodynamic parameters indicate the spontaneous and endothermic nature of the process. The uptake of Cr(VI) increases as pH decreases and the maximum removal has been attributed to the formation of positively charged aquacomplexes of iron at the surface and a subsequent interaction with the dominant HCrO4 ‐species. An empirical equation has been developed to predict equilibrium adsorption capacity from knowledge of equilibrium adsorbate concentration.

Treatment of Cadmium(I)-Rich Effluents (Kinetic Modelling and Mass Transfer)

Abstract Removal of Cd(II) by sorption on China clay has been investigated. Removal increased from 41.0 to 80.3% by decreasing the cadmium concentration from 2.0 × 10−4 M to 0.5 × 10−4 M at pH = 6.5 and 30°C. Kinetic modelling of the process has been done using Lagergrens first-order rate equation. The rate of adsorption at pH = 6.5 and 30°C was found to be 5.0 × 10−2 min−1. The process of removal involves intraparticle diffusion. Mass transfer parameters have been calculated; the process is exothermic in nature. Studies with representative wastewater samples from plating units have also been undertaken.

Synthesis and characterisation of some complexes of manganese(II) and iron(II) picrates with heterocyclic amines

SummaryComplexes of manganese(II) and iron(II) picrates with various bidentate (L) and monodentate (L′) heterocyclic bases have been synthesised; their compositions have been established as [ML3]A2 (1), [ML2 · 2 H2O]A2 (2), [ML′6]A2 (3) and [ML′4 · 2 H2O]A2 (4), where M = FeII and MnII, L = 2,2′-bipyridyl (bipy) and 1,10-phenanthroline (phen) in (1), A = picrate anion; M = MnII, L = bipy and phen in (2); M = FeII, L′ = pyridine (py), 4-picoline (4-pic) and 3-picoline (3-pic) in (3); M = MnII, L′ = py, 4-pic, quinoline (quin) and 2,6-lutidine (2,6-lut) in (4) and also M = FeII, L′ = quin and 2,6-lut.

Cationic complexes of chelated bis(η-cyclopentadienyl)titanium(IV) with halometallates of gallium(III), indium(III) and thallium(III)

SummaryEight complexes of the chelated bis(η-cyclopenta-dienyl)titanium(IV) cation. [η-Cp2TiL][MX4] (L = acetyl-acetone, M = GaIII, InIII or TiIII: X = Cl, Br or I) have been isolated from aqueous solution and characterised by elemental analyses and i.r. data. Their ionic nature has been confirmed by conductance measurements.