Srinivasa R. Popuri

A study on the recycling of scrap integrated circuits by leaching

In order to minimize the problem of pollution and to conserve limited natural resources, a method to recover the valuable metals such as gold, silver and copper) present in the scrap integrated circuits (ICs) was developed in the present study. Roasting, grinding, screening, magnetic separation, melting and leaching were adopted to investigate the efficiency of recovery of gold, silver and copper from scrap ICs. The collected scrap IC samples were roasted at 850°C to destroy their plastic resin sealing material, followed by screening and magnetic separation to separate the metals from the resin residue. The non-ferrous materials (0.840 mm) were mainly composed of copper and could be melted into a copper alloy. Non-ferrous materials containing gold (860.05 ppm), silver (1323.12 ppm) and copper (37259.7 ppm) (size less than 50 mesh) were recovered 100% by a leaching process and thiourea was used as a leaching reagent.

Removal of copper (II) ions from aqueous solutions onto chitosan/carbon nanotubes composite sorbent

AbstractCarbon nanotubes (CNTs) have been considered as promising materials in various applications including water treatment. Manipulation of CNT’s with polymer offers unique properties as a composite in treatment of wastewater and removal of heavy metal ions. In the present work, we have developed a chitosan (CS)/multiwall carbon nanotubes (MWCNTs) composite sorbent by mixing the naturally occurring biopolymer CS and functionalized MWCNTs in 1% acetic acid solution. The obtained composite adsorbent was used successfully for the removal of copper (II) ions from aqueous solutions. The influence of variable parameters like pH, concentration of the metal ion, amount of adsorbent, and contact time on the extent of adsorption was investigated by batch method. Graphical correlations of various adsorption isotherm models such as Langmuir and Freundlich have been carried out. The data were analyzed by the Lagergren pseudo-first-order and pseudo-second-order kinetic models. Further the adsorption performance of t...

Effect of Solvent on Physico-Chemical Properties and Antibacterial Activity of Chitosan Membranes

Chitosan is widely used in various applications such as pharmaceutical, medical, wastewater treatment (WWTR), and antibacterial. Modifying chitosans properties is still attractive in scientific and industrial research. The acid solvation effect on the antibacterial activity (ABA) and physico-chemical properties of chitosan membranes synthesized via the solution casting-solvent evaporation technique was investigated. Various acids such as acetic, ascorbic, citric, glycolic, maleic, oxalic, and tartaric acid were used as chitosan solvents and membrane properties were characterized by Fourier transform infrared spectroscopy-attenuated total reflectance (FTIR-ATR) in order to study chemical interaction between the acid solvent and the shift of carbonyl and amine groups. Thermogravimetric analysis (TGA), static swelling, membrane thickness, and tensile strength experiments also characterized the membranes’ physical, chemical, and thermal properties. Further, the effect of acid solvation on the ABA of chitosan membranes for WWTR was interrogated with Escherichia coli and acetic acid solvated chitosan membrane exhibited highest ABA (99%).

Resource recovery of scrap silicon solar battery cell

In order to minimize pollution problems and to conserve limited natural resources, a hydrometallurgical procedure was developed in this study to recover the valuable resources of silicon (Si), silver (Ag) and aluminum (Al) from scrap silicon solar battery cells. In this study, several methods of leaching, crystallization, precipitation, electrolysis and replacement were employed to investigate the recovery efficiency of Ag and Al from defective monocrystalline silicon solar battery cells. The defective solar battery cells were ground into powder followed by composition analysis with inductively coupled plasma-atomic emission spectrometry. The target metals Ag and Al weight percentage were found to be 1.67 and 7.68 respectively. A leaching process was adopted with nitric acid (HNO3), hydrochloric acid, sulfuric acid (H2SO4) and sodium hydroxide as leaching reagent to recover Ag and Al from a ground solar battery cell. Aluminum was leached 100% with 18N H2SO4 at 70°C and Ag was leached 100% with 6N HNO3. Pure Si of 100% was achieved from the leaching solution after the recovery of Ag and Al, and was analyzed by scanning electron microscope-energy dispersive spectroscopy. Aluminum was recovered by crystallization process and silver was recovered by precipitation, electrolysis and replacement processes. These processes were applied successfully in the recovery of valuable metal Ag of 98–100%.

Enhanced surface functionality and microbial fuel cell performance of chitosan membranes through phosphorylation

The effects of plasticization and cross-linking on the performance of chitosan as promising proton exchange membranes (PEMs) for bioelectricity generation in microbial fuel cells (MFCs) were investigated. The physico-chemical properties of chitosan (CS), sorbitol-chitosan (S-CS), phosphorylated-chitosan (CS-P) and phosphorylated-sorbitol-chitosan (S-CS-P) membranes were investigated by FESEM-EDS, FTIR-ATR, XRD, TGA, tensile strength and sorption studies. The performance of the fabricated PEMs was assessed by power density and cation exchange capacity (CEC). Maximum power densities achieved were 130.03, 20.76, 94.59 and 7.42mW/m(2) for CS-P, S-CS-P, S-CS and CS membranes respectively. Phosphorylation of the CS membranes increased CEC and tensile strength, attributed to an increase in bonded amide and phosphate ionic surface groups. Further, 49.07% COD removal from municipal wastewater was achieved with CS-P membranes. Thus, through chemical modifications, the physico-chemical and mechanical properties of natural abundant biopolymer chitosan can be enhanced for its use as an environmentally sustainable PEM in MFC technology.

Evaluation of Antibacterial Activity and Characterization of Synthesized Biodegradable Copolymers

Green copolymer Poly(MA-CA) was developed by the thermal condensation polymerization of monomers such as DL-Malic acid (MA) and Citric acid (CA). The copolymer of Poly(MA-CA) was synthesized by varying the ratio of MA and CA monomers with 1:0, 1:3, 1:1, 3:1 and 0:1, and their antibacterial properties were studied with respect to their activity on Gram-positive and Gram-negative bacteria by the bacterial count method. Furthermore, the biocidal activity of the plain monomers was also investigated and compared to those of the copolymers. Synthesized copolymers show good antibacterial effects towards both Gram-positive and Gram-negative bacteria. The antimicrobial properties of the copolymers and the monomers were studied by varying the ratio of polymers, effect of polymer concentration and effect of pH. Results indicated that the antibacterial activity of the copolymers increased with MA content and polymer dose. At low content of MA (wt.%), the copolymers poly(MA-CA)(1:3) possessed a higher effect on Gram-positive bacteria Bacillus cereus and Micrococcus luteus than Gram-negative bacteria Salmonella and Shigella. The other copolymers with the ratio of 1:1 and 3:1 including MA homopolymer possesses 100% inhibition of both Gram-positive and Gram-negative bacteria under the conditions studied. The developed polymers were extensively characterized by Fourier transform infrared spectroscopy analysis, thermal gravimetric analysis, X-ray diffraction analysis and scanning electron microscope-energy dispersive spectroscopy to understand their physicochemical properties.

Simultaneous wastewater treatment and bioelectricity production in microbial fuel cells using cross-linked chitosan-graphene oxide mixed-matrix membranes

Microbial fuel cells (MFCs) are emerging technology for wastewater treatment by chemical oxygen demand (COD) reduction and simultaneous bioelectricity production. Fabrication of an effective proton exchange membrane (PEM) is a vital component for MFC performance. In this work, green chitosan-based (CS) PEMs were fabricated with graphene oxide (GO) as filler material (CS-GO) and cross-linked with phosphoric acid (CS-GO-P(24)) or sulfuric acid (CS-GO-S(24)) to determine their effect on PEM properties. Interrogation of the physicochemical, thermal, and mechanical properties of the cross-linked CS-GO PEMs demonstrated that ionic cross-linking based on the incorporation of PO43− groups in the CS-GO mixed-matrix composites, when compared with sulfuric acid cross-linking commonly used in proton exchange membrane fuel cell (PEMFC) studies, generated additional density of ionic cluster domains, rendered enhanced sorption properties, and augmented the thermal and mechanical stability of the composite structure. Consequently, bioelectricity performance analysis in MFC application showed that CS-GO-P(24) membrane produced 135% higher power density than the CS-GO-S(24) MFC system. Simultaneously, 89.52% COD removal of primary clarifier municipal wastewater was achieved in the MFC operated with the CS-GO-P(24) membrane.

Biosorption Performance of Biodegradable Polymer Powders for the Removal of Gallium(III) ions from Aqueous Solution

Abstract Gallium (Ga) is considered an important element in the semiconducting industry and as the lifespan of electronic products decrease annually Ga-containing effluent has been increasing. The present study investigated the use of biodegradable polymer powders, crab shell and chitosan, in the removal of Ga(III) ions from aqueous solution. Ga(III) biosorption was modeled to Lagergren-first, pseudo-second order and the Weber-Morris models. Equilibrium data was modeled to the Langmuir, Freundlich and Langmuir-Freundlich adsorption isotherms to determine the probable biosorption behavior of Ga(III) with the biosorbents. The biosorbents were investigated by Fourier Transform Infrared Spectroscopy, X-ray Diffraction and Scanning Electron Microscopy/Energy Dispersive Spectra analysis.

Preparation of High-Purity Ultrafine Copper Powder in Mass-Production by Chemical Reduction Method: Taguchi Robust Design Optimization

The Taguchi robust design method is implemented for the optimization of experimental conditions in the synthesis of high-purity ultrafine copper powder (HUCP) in mass-production by the chemical reduction method. A reducing agent, reaction temperature, reducing agent weight, and a stirring rate are chosen as the major optimization factors and the conversion rate, particle size, and reaction time are chosen as the desired targets. It is established that the reducing agent and the reaction temperature are the most significant factors that affect the desired targets. Among the selected or designed factors, the optimal conditions for producing the HUCP are: NaH2PO2 · H2O as the reducing agent (level 2), temperature 70°C (level 3), a reducing agent weight of 8.14 kg (level 3), and a stirring rate 300 rpm (level 2). The study results for the three desired targets are in agreement with the prediction made by the Taguchi method. Furthermore, the pure (impurity <0.06%) facecentered cubic structure of the HUCP with 1.51 μm average particle size is extensively characterized and determined by inductively coupled plasma–optical emission spectrometer (ICP–OES), laser particle-size analyzer (DLS), scanning electron microscopy (SEM), and X-ray diffraction (XRD) analysis. This surfactant-free facility method is suitable for the synthesis of highpurity ultrafine copper powder by mass-production method.

Biosorption of Ni(II) from aqueous solutions by Syzygium cumini bark powder: Equilibrium and kinetic studies

Abstract The present work deals with the use of Syzygium cumini bark powder as a biosorbent for Ni(II) removal from aqueous solution. The biosorption characteristics of Ni(II) onto S. cumini bark powder was investigated as a function of pH, contact time, biosorbent dosage, and initial Ni(II) ion concentration. Langmuir and Freundlich isotherms were used to fit the experimental data. The best interpretation for the equilibrium data was given by the Langmuir isotherm. The maximum biosorption capacity was found to be 294.1 mg/g for Ni(II) at pH 5.0 and at room temperature. The biosorbent was characterized by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy analyses. The equilibrium biosorption data were well fitted with the pseudo-second-order kinetic equation. The chi-square (χ2) and sum of the square error tests were also carried out to find the best-fit biosorption isotherm and kinetic model. The FTIR results revealed that carboxyl, hydroxyl, and amine groups are responsible...