AUTOMORPHISMS AND PROPER BASES IN SPACE OF ANALYTIC FUNCTIONS OF SEVERAL COMPLEX VARIABLES REPRESENTED BY DIRICHLET SERIES(*)

Srivastava, J.K.,Srivastava, Rajiv K. Department of Mathematics 1981 Kyungpook mathematical journal Vol.21 No.2

Novel Aqueous Processing of the Reverted Turbine-Blade Superalloy for Rhenium Recovery

Srivastava, Rajiv Ranjan,Kim, Min-seuk,Lee, Jae-chun American Chemical Society 2016 INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH - Vol.55 No.29

<P>A preliminary study on the hydrometallurgical recovery of rhenium from an engine-reverted superalloy, CMSX-4, was performed. The novelty of this work dealt with (i) the applicability of electro-generated Cl-2 in rhenium leaching and (ii) the maneuvering of the organic extractants based on the metal speciation in leach liquor. In a two-step HC1 leaching, more than 98% rhenium was selectively leached in the presence of dissolved chlorine (Cl-2aq. and Cl-3aq(-)) in the second step, which Was performed after a leaching of thermal-barrier and base-alloy elements in 4 mol L-1 HC1. The leaching kinetics of rhenium indicated a shift from surface diffusion to a chemically controlled reaction with a variance in temperature from 313 to 353 K. The first use of phosphinic acid in molybdenum separation from rhenium in the leach liquor yielded a high separation value (beta(Mo/Re) = 839) using 0.067 mol L-1 extractant; whereas the mixed-phosphine oxides showed a tremendous selectivity for separating rhenium from the base-metal impurities in the Mo-depleted solution. The extraction of rhenium increased from 9% to 98% with an increase in extractant concentration from 0.005 to 0.08 mol L-1 in the organic phase. On a metal-to-metal basis, the recovery value of 93% rhenium as NH4ReO4 (9.5 g L-1 Re in the solution) demonstrated the potential of the present process.</P>

Solvent extraction of gold from a chloride-hypochlorite leached solution of waste printed circuit boards

Srivastava Rajiv Ranjan,Ilyas Nimra 한국자원공학회 2023 Geosystem engineering Vol.26 No.5

This study reveals the reclamation process of gold from a brine-leached solution of waste printed circuit boards (WPCBs) after the maximum leaching of base metals in a nitric acid medium. The brine leaching performed in the presence of hypochlorite yielded leach liquor of 152 ppm Au, 86 ppm, Cu, and 62 ppm Ni that underwent solvent extraction with tri-butyl phosphate (TBP) in Exxol D80. The gold extraction process was observed to be selective over base metal impurities, while the effect of TBP concentration, equilibrium pH, temperature, and organic-to-aqueous phase ratio was optimized. Experimental results showed the formation of ½HAuCl4 � 2TBP:H2O� complex into the extraction phase with the negative enthalpy change value of −98.7 kJ/mol. Thiosulphate mobilized stripping of gold from the loaded-TBP could give about 99% recovery efficiency of the solvent extraction process along with a good regeneration of the organic extractant to be re-used.

Qualitative and Quantitative Comparison of Contrast-Enhanced Fluid-Attenuated Inversion Recovery, Magnetization Transfer Spin Echo, and Fat-Saturation T1-Weighted Sequences in Infectious Meningitis

Rajiv Azad,Mohit Tayal,Sheenam Azad,Garima Sharma,Rajendra Kumar Srivastava 대한영상의학회 2017 Korean Journal of Radiology Vol.18 No.6

Objective: To compare the contrast-enhanced fluid-attenuated inversion recovery (CE-FLAIR), the CE T1-weighted (CE-T1W) sequence with fat suppression (FS) and magnetization transfer (MT) for early detection and characterization of infectious meningitis. Materials and Methods: Fifty patients and 10 control subjects were evaluated with the CE-FLAIR and the CE-T1W sequences with FS and MT. Qualitative assessment was done by two observers for presence and grading of abnormal leptomeningeal enhancement. Quantitative assessment included computation of net meningeal enhancement, using single pixel signal intensity software. A newly devised FLAIR based scoring system, based on certain imaging features including ventricular dilatation, ependymal enhancement, infarcts and subdural effusions was used to indicate the etiology. Data were analysed using the Student’s t test, Cohen’s Kappa coefficient, Pearson’s correlation coefficient, the intraclass correlation coefficient, one way analysis of variance, and Fisher's exact test with Bonferroni correction as the post hoc test. Results: The CE-FLAIR sequence demonstrated a better sensitivity (100%), diagnostic accuracy (95%), and a stronger correlation with the cerebrospinal fluid, total leukocyte count (r = 0.75), protein (r = 0.77), adenosine deaminase (r = 0.81) and blood glucose (r = -0.6) values compared to the CE-T1W sequences. Qualitative grades and quantitative meningeal enhancement on the CE-FLAIR sequence were also significantly greater than those on the other sequences. The FLAIR based scoring system yielded a diagnostic accuracy of 91.6% and a sensitivity of 96%. A strong inverse Pearson’s correlation (r = -0.95) was found between the assigned score and patient’s Glasgow Coma Scale at the time of admission. Conclusion: The CE-FLAIR sequence is better suited for evaluating infectious meningitis and could be included as a part of the routine MR imaging protocol.

금이 함유된 왕수용액으로부터 TBP(tributyl phosphate) 용매추출에 의한 질산과 금의 분리

배무기,Rajiv Ranjan Srivastava,김수경,이재천 한국자원리싸이클링학회 2017 資源 리싸이클링 Vol.26 No.1

TBP(tributyl phosphate)를 사용하여 왕수 침출액으로부터 질산과 금을 추출하여 회수하는 공정을 개발하기 위한기초연구가 수행되었다. 순수한 왕수용액으로부터 추출제의 농도, 질산과 염산의 농도 비에 따른 질산의 추출거동을 조사하였으며, 금을 함유하는 왕수용액으로부터 질산과 금의 추출율을 구하였다. McCabe-Thiele 도로부터 얻어진 조업단수와 상비로 역류추출을 행하여 이론적인 추출단수를 검증하였다. 유기상에 장진된 질산과 금의 연속적인회수를 위한 탈거실험을 수행하였다. 질산과 금의 추출과 염산의 영향을 고려하여 O/A = 1:0.85의 조건으로 역류추출을 통해 2단에 의해 103.0 mg·L .1 의 금은 99.9% 추출되었으며, 3단에 의해 151.2 g·L .1 의 질산은 98.0% 추출되었다. 질산과 금의 탈거제로는 증류수와 티오황산나트륨이 사용되었으며 탈거율은 각각 99.5%, 92.0%이었다. 이와같은 연구결과로 왕수용액에 함유되어 있던 금과 질산을 동시에 추출하고 연속적인 탈거공정에 의해서 질산과 금을 회수하는 것이 가능함을 확인하였다. The present study to develop a process for extracting nitric acid and gold from aqua regia leach solution using TBP(tributyl phosphate) was conducted. The pure aqua regia was used to investigate the extractive behavior of nitric acid depending on the concentration of extractant, concentration ratio of nitric and hydrochloric acid. The extraction rate of nitric acid and gold from the gold bearing aqua regia was also examined. The theoretical extraction number was verified by counter current using the number of operations and the phase ratio obtained from McCabe-Thiele diagram. Stripping experiments were carried out for continuous recovery of nitric acid and gold in loaded organic. Considering the effect of extraction acid and gold, the simulation showed that greater than 99.9% extraction of 103.0 mg·L −1gold and 98.0% of 151.2 g·L −1 nitric acid could be attained in a two and three-stage counter-current extraction at an O/A phase ratio of 1:0.85. Distilled water and sodium thiosulfate were used as the nitric acid and gold stripping solution. The stripping rates were 99.5% and 92.0%, respectively. The study revealed that the recovery of nitric acid and gold from gold bearing aqua regia was a plausible approach through simultaneous extraction and continuous stripping of nitric acid and gold.

Liquid–liquid separation of copper and nickel ammine complexes using phenolic oxime mixture with tributyl phosphate

Ilyas Sadia,Srivastava Rajiv Ranjan,Jin Suhyeon,Kim Hyunjung 한국자원공학회 2023 Geosystem engineering Vol.26 No.2

In the present study, a complete separation of copper over nickel has been studied from an ammoniacal leach liquor of nickel laterite ore generated via the Caron process. For this purpose, a phenolic oxime (LIX 84-IC) used as the extractant molecule was mixed with tributyl phosphate (TBP) to inhibit the co-extraction of nickel with copper loading into the organic phase. The antagonistic effect of TBP was confirmed by the distribution coefficients to be Dmix << DLIX 84-IC + DTBP and negative values of ΔD. The highest separation (βCu/Ni) of >1329 was yielded using the molar ratio of organic mixture at LIX 84-IC:TBP = 0.4:0.6 at an organic-to-aqueous phase ratio of 1. The thermodynamic properties of copper extraction exhibited an endothermic nature with ΔH° value of 5.4 kJ∙mol−1, indicating the formation of inner-sphere coordination between metal ions and the organic mixture. Further, the stripping of copper from the loaded organic phase was quantitatively achieved by contacting with 1.0 mol∙L−1 H2SO4 solution at the unit phase ratio.

Growth projections against set-target of renewable energy and resultant impact on emissions reduction in India

Karan Chabhadiya,Rajiv Ranjan Srivastava,Pankaj Pathak 대한환경공학회 2021 Environmental Engineering Research Vol.26 No.2

In accordance with the Paris Climate Agreement (COP21) and Sustainable Development Goals (SDGs), India is greatly focused on deployment of renewable energy (RE) for supplementing the energy requirements of the country. The present article assesses the validity of the promises offered by RE technologies in India and its necessary action to understand the gap between setting goals and the ground situation, which can also show a pathway to other developing countries. Therefore, the long-term projection perspectives on RE growth have been made using the India Energy Security Scenario-2047. In order to achieve the set target for emissions reduction of greenhouse gases (GHGs) i.e., 1209 MT CO2e in support of SDGs to the 2005 level by 2030, three renewable growth scenarios have been tested for transitioning the Indian energy system. Accordingly, the regression analysis reveals that the most desirable growth scenario will require a steady rise of RE contribution in the overall energy mix of India by 2030 from the current ~21% to 68% of the installed capacity. In this view, the present study highlights the exploration of new alternatives in long-term energy planning, and less on one-sided scenario to achieve the emissions’ reduction target.

Hydrometallurgical recovery of critical metals from an incinerated fly ash of municipal solid waste from western India

Desai Yuti,Srivastava Rajiv Ranjan,Srivastava Vijay Kumar,Kaushik Geetanjali,Singh Vinay Kumar 한국자원공학회 2023 Geosystem engineering Vol.26 No.5

The global generation of 2.2 billion tons of municipal solid waste (MSW) as a result of population growth, rapid urbanization, and industrial development has highlighted an urgent need for MSW management. Incineration is widely accepted as one alternative to landfilling; however, the recovery of heavy metals from the incinerated fly ash (IFA) before its final disposal is highly desirable to make the process sustainable. In this study, we studied the recovery of zinc and lead from typical MSW-IFA employing hydrometallurgical techniques. Sulfuric acid leaching was performed to selectively leach out zinc over the lead at the optimal condition of H2SO4 concentration = 1.5 M, temperature = 30°C, S/L ratio = 150 g/L, time = 2 h, and stirring speed = 300 rpm. The sulfate leach liquor was treated with a 5% stoichiometric excess of oxalic acid to precipitate>99% of zinc to be recovered as ZnC2O4·2 H2O. Further, the remaining lead in leach residue was subsequently leached in 50 g/L NaCl solution for 2 h yielded>94% efficiency. The dissolved lead was crystallized to recover the crystals of PbCl2. The demonstrated process leads towards the recovery of critical metals from an alternative source of MSW-IFA.

Simple recycling of copper by the synergistic exploitation of industrial wastes: a step towards sustainability

Jun, Minji,Srivastava, Rajiv Ranjan,Jeong, Jinki,Lee, Jae-chun,Kim, Min-seuk The Royal Society of Chemistry 2016 Green chemistry Vol.18 No.13

<P>A 'Green Recycling' process for copper recovery by the synergistic treatment of two different industrial wastes is presented. Firstly, the solid waste generated during the processing of epoxy modeling compounds was treated with the waste nitric acid solution produced in the sputter cleaning. A faster leaching rate of copper without any effect of temperature was noticed, which can be attributed to the intermediate-controlled kinetics along with the autocatalytic behaviour of Cu2+ present in the waste solution. An increase in pulp density above 25% adversely affected the solubilisation of copper because of the decreased lixiviant acidity corresponding to the metals being leached. Subsequently, the key experimental parameters for liquid-liquid separation of copper using LIX 84-I after Fe-removal with D2EHPA, viz. equilibrium pH, extractant concentration, temperature, and phase ratio (O/A), were optimized and correlated with complexation chemistry. The extraction equilibrium constant (log K-ex = 1.67) under the studied conditions of nitrate media was determined by the log-log plot of D-star[H+](aq)(2) vs. ([HR](2))(org) Thermodynamic properties indicated a strong affinity of LIX 84-I towards Cu2+ due to the emergence of spontaneous inner-sphere coordination with disrupted hydration. A counter-current study for the separation and recovery of copper was performed under the optimized conditions, which has successfully validated the results of extraction and stripping isotherms exhibited by the McCabe-Thiele plots. The unfolded hydro-metallurgical process described in this study has a potential for sustainable utilization of wastes to recover the metal of interest at a 46% lower energy cost than the processing of primary ores.</P>

Hydrometallurgical recycling of surface-coated metals from automobile-discarded ABS plastic waste

Kim, Tai Gyun,Srivastava, Rajiv R.,Jun, Minji,Kim, Min-seuk,Lee, Jae-chun Elsevier 2018 waste management Vol.80 No.-

<P><B>Abstract</B></P> <P>The ammoniacal leaching of surface-coated metals from automobile-discarded ABS plastics followed by their recovery through solvent extraction has been investigated. The leaching of ABS (typically containing 4.1% Cu, 1.3% Ni, and 0.03% Cr) could efficiently dissolve the ammine complexes of Cu and Ni, leaving Cr unleached as fine particles. The optimization studies for achieving the maximum efficiency revealed that the leaching of metal ions in different ammoniacal solutions follows the order CO<SUB>3</SUB> <SUP>2−</SUP> > Cl<SUP>−</SUP> > SO<SUB>4</SUB> <SUP>2−</SUP>. The leaching carried out in a carbonate medium by maintaining the total NH<SUB>3</SUB> concentration 5.0 M at a NH<SUB>4</SUB>OH/(NH<SUB>4</SUB>)<SUB>2</SUB>CO<SUB>3</SUB> ratio of 4:1, pulp density of 200 g/L, agitation speed of 400 rpm, temperature of 20 °C, and time of 120 min yielded the optimum efficiency of >99% Cu and Ni (i.e., 8.14 g/L and 2.57 g/L, respectively, in the leach liquor). Subsequently, the solvent extraction of metals from ammoniacal leach liquor as a function of extractant (LIX 84-I) concentration and organic-to-aqueous (O:A) phase ratio was examined. Based on the extraction data, a three-stage counter-current extraction at O:A = 1:1 was validated using 0.8 M LIX 84-I, yielding the quantitative extraction of both metals into the organic phase. Thereafter, the stripping of metals in acid solutions indicated that 0.5 M H<SUB>2</SUB>SO<SUB>4</SUB> could quantitatively strip Ni from the loaded organic phase; however, ∼27% Cu was also co-stripped. The rest of Cu from the Ni-depleted organic phase was separately stripped with 1.0 M H<SUB>2</SUB>SO<SUB>4</SUB> that can be directly sent to the electrowinning process. On the other hand, the co-stripped metals from the acidic solution can be easily separated, again using LIX 84-I as the extractant, by adopting the pH-swing method. Finally, a process has been proposed for the hydrometallurgical recovery of surface-coated metals from waste ABS plastics; that does not affect the physicochemical characteristics of the polymer substances for their reuse.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A recycling scheme for the sustainable management of waste ABS plastics is reported. </LI> <LI> Ammoniacal leach of surface-coated metals of material leaves native ABS unaffected. </LI> <LI> Cu and Ni leaching in ammonia salt solutions follows the order: CO<SUB>3</SUB> <SUP>2−</SUP> > Cl<SUP>−</SUP> > SO<SUB>4</SUB> <SUP>2−</SUP>. </LI> <LI> LIX 84-I yields promising selectivity in solvent extraction and stripping of Cu & Ni. </LI> <LI> The disclosed hydrometallurgical process ensures recovery of metals of >99%. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>