Heavy metal removal from water by adsorption using a low-cost geopolymer.

In the present study, a geopolymer from dolochar ash was synthesized and used for the removal of heavy metal ions such as Co(II), Ni(II), Cd(II), and Pb(II) from the aqueous solution through the adsorption process. The geopolymer was characterized by a series of analytical techniques. The XRD pattern revealed the loss of dolochar ash crystallinity on geoploymerization. The peak at 982 cm-1 observed in the FTIR spectrum due to Si-O-Si and Si-O-Al bonds confirmed the formation of geopolymer. BET surface area analyses indicated the mesoporous nature of the sample. The adsorption experiments revealed the higher removal efficiency of the geopolymer in comparison with the feed dolochar ash. The effects of different experimental factors such as pH, temperature, reaction time, and initial concentration of metal ions on metal uptake efficiency were evaluated to optimize the removal efficiency. The maximum removal of 98-99% was achieved when the pH, temperature, and initial metal ion concentration were 7.8, 343 K, and 10 ppm, respectively. The adsorption process followed the pseudo-second-order rate equation and validated the Langmuir adsorption model. Thermodynamic parameters such as ΔH, ΔS, and ΔG confirmed that the process to be spontaneous and endothermic. This geopolymer was found to compete efficiently with many adsorbents reported in the literature for water treatment.

Maximizing biomass productivity and CO2 biofixation of microalga, Scenedesmus sp. by using sodium hydroxide.

A series of experiments were carried out with three native strains of microalgae to measure growth rates, biomass, and lipid productivities. Scenedesmus sp. IMMTCC-6 had better biomass growth rate and higher lipid production. The growth, lipid accumulation, and carbon dioxide (CO2) consumption rate of Scenedesmus sp. IMMTCC-6 were tested under different NaOH concentrations in modified BBM. The algal strain showed the maximum specific growth rate (0.474/day), biomass productivity (110.9 mg l(-1) d(-1)), and CO2 consumption rate (208.4 mg l(-1) d(-1)) with an NaOH concentration of 0.005 M on the 8(th) day of cultivation. These values were 2.03-, 6.89-, and 6.88-fold more than the algal cultures grown in control conditions (having no NaOH and CO2). The CO2 fixing efficiency of the microalga with other alternative carbon sources like Na2CO3 and NaHCO3 was also investigated and compared. The optimized experimental parameters at shake-flask scale were implemented for scaling up the process in a self-engineered photobioreactor. A significant increase in lipid accumulation (14.23% to 31.74%) by the algal strain from the logarithmic to stationary phases was obtained. The algal lipids were mainly composed of C16/C18 fatty acids, and are desirable for biodiesel production. The study suggests that microalga Scenedesmus sp. IMMTCC-6 is an efficient strain for biodiesel production and CO2 biofixation using stripping solution of NaOH in a cyclic process.

Treatment of electronic waste to recover metal values using thermal plasma coupled with acid leaching--a response surface modeling approach.

The global crisis of the hazardous electronic waste (E-waste) is on the rise due to increasing usage and disposal of electronic devices. A process was developed to treat E-waste in an environmentally benign process. The process consisted of thermal plasma treatment followed by recovery of metal values through mineral acid leaching. In the thermal process, the E-waste was melted to recover the metal values as a metallic mixture. The metallic mixture was subjected to acid leaching in presence of depolarizer. The leached liquor mainly contained copper as the other elements like Al and Fe were mostly in alloy form as per the XRD and phase diagram studies. Response surface model was used to optimize the conditions for leaching. More than 90% leaching efficiency at room temperature was observed for Cu, Ni and Co with HCl as the solvent, whereas Fe and Al showed less than 40% efficiency.

Molecular modeling studies of poly lactic acid initiation mechanisms.

The two possible routes to synthesize poly (lactic acid) are polycondensation of the lactic acid and ring opening polymerization (ROP) of the lactide. This work involves molecular modeling of the polymerization initiation mechanisms using different initiators a) H(2)SO(4) for polycondensation b) aluminum isopropoxide for coordination-insertion ROP c)methyl triflate for cationic ROP, and d) potassium methoxide for anionic ROP. For molecular modeling of PLA, we have benchmarked our approach using Ryner's work on ROP of L-lactide using stannous (II) 2-ethylhexanoate (Sn(Oct)(2)) and methanol as initiators. Our values of -15.2 kcal mol(-1) and -14.1 kcal mol(-1) for enthalpy changes in the two steps of activated complex formation match with Ryner's. Geometric and frequency optimizations have been done on Gaussian'03 using B3LYP density functional theory along with the basis sets LANL2DZ for metal atoms and 6-31G* and 6-31G** for non metal atoms. The kinetic rate constant for each mechanism has been calculated using the values of energy of activation, change in enthalpy, Gibbs free energy, entropy and the partition functions from the Gaussian'03 output. Our polycondensation rate constant value of 1.07 x 10(-4) se(-1) compares well with 1.51 x 10(-4) se(-1) as reported by Wang. However, ROP rate constants could not be validated due to lack of experimental data.