K.K. Sahu

An overview of the recovery of acid from spent acidic solutions from steel and electroplating industries

Every metal and metallurgical industry is associated with the generation of waste, which may be a solid, liquid or gaseous in nature. Their impacts on the ecological bodies are noticeable due to their complex and hazardous nature affecting the living and non-living environment which is an alarming issue to the environmentalist. The increasingly stringent regulations regarding the discharge of acid and metal into the environment, and the increasing stress upon the recycling/reuse of these effluents after proper treatment have focused the interest of the research community on the development of new approaches for the recovery of acid and metals from industrial wastes. This paper is a critical review on the acidic waste streams generated from steel and electroplating industries particularly from waste pickle liquor and spent bleed streams. Various aspects on the generation of these streams and the methods used for their treatment either for the recovery of acid for reuse or disposal are being dealt with. Major stress is laid upon the hydrometallurgical methods such as solvent extraction.

Extractive removal of chromium (VI) from industrial waste solution

Extractive removal of Cr (VI) was carried out from chloride solutions using cyanex 923 mixed with kerosene. The efficiency of this extractant was studied under various experimental conditions, such as concentration of different mineral acids in the aqueous phase, concentration of cyanex 923 and Cr (VI) present in the initial aqueous feed, temperature and time of extraction, organic to aqueous (O/A) phase ratio. Percentage Cr (VI) extraction decreases with the increase in temperature at varying concentration of cyanex 923. The interference of the impurities usually associated with Cr (VI) such as Cr (III), Cu, Ni, Fe (II), Zn, Chloride and sulphate, etc., were examined under the optimized conditions and only Zn was found to interfere. Under the optimum experimental conditions 98.6-99.9% of Cr (VI) was extracted in 3-5 min at O/A of 2 with the initial feed concentration of 1g/L of Cr (VI). The extracted Cr (VI) was quantitatively stripped with 1M NaOH and the organic phase obtained after the stripping of Cr (VI) was washed with dilute HCl solution to neutralize any NaOH trapped/adhered to the solvent and then with distilled water. This regenerated solvent was reused in succeeding extraction of chromium (VI). Finally a few experiments were performed with the synthetic effluent from an electroplating industry.

Hazardous waste to materials: recovery of molybdenum and vanadium from acidic leach liquor of spent hydroprocessing catalyst using alamine 308.

Recovery of valuable materials/metals from waste goes hand in hand with environmental protection. This paper deals with the development of a process for the recovery of metals such as Mo, V, Ni, Al from spent hydroprocessing catalyst which may otherwise cause a nuisance if dumped untreated. A detailed study on the separation of molybdenum and vanadium from the leach solution of spent hydroprocessing catalyst of composition: 27.15% MoO₃, 1.7% V₂O₅, 3.75% NiO, 54.3% Al₂O₃, 2.3% SiO₂ and 10.4% LOI is reported in this paper. The catalyst was subjected to roasting under oxidizing atmosphere at a temperature of about 550 °C and leaching in dilute sulphuric acid to dissolve molybdenum, vanadium, nickel and part of aluminium. Metals from the leach solution were separated by solvent extraction. Both molybdenum and vanadium were selectively extracted with a suitable organic solvent leaving nickel and dissolved aluminium in the raffinate. Various parameters such as initial pH of the aqueous feed, organic to aqueous ratio (O:A), solvent concentration etc. were optimized for the complete extraction and recovery of Mo and V. Molybdenum and vanadium from the loaded organic were stripped by ammonia solution. They were recovered as their corresponding ammonium salt by selective precipitation, and were further calcined to get the corresponding oxides in pure form.

Kinetic studies on the exchange of bivalent metal ions on amberlite IRC-718: An iminodiacetate resin

Abstract The rate of uptake of alkaline earth metals, copper, and lead have been investigated by a chelating ion exchange resin containing iminodiacetic acid as ligand attached to the copolymer of styrene and divinyl benzene of macroporous matrix structure. It binds alkaline earth metals, Cu, and Pb by the formation of chelate complexes with the carboxylate group of this resin. The experiments discussed in this work have allowed to establish the paramount importance of the presence of this chelating group in obtaining practically useful rates of metal ion uptake. The kinetic parameters like diffusion coefficient (D o), activation energies (ΔE a) and entropy of activation have been evaluated under the conditions favoring a particle diffusion control mechanism and the study followed the three models i.e., Nernst Planck, B t technique and Ash model. K d values in demineralised water (DMW) were found in the order Cu2+ > Pb2+ > Mg2+ > Sr2+ > Ba2+ > Ca2+.

Influence of Temperature on the Exchange of Alkaline Earth and Transition Metals on Iminodiacetate Resin

Abstract Ion exchange equilibrium studies were carried out for Mg2+, Ba2+, Ca2+, Sr2+, Cu2+, Pb2+, Hg2+, Ag+, Mn2+, Ni2+, Fe3+ ions using Amberlite IRC 718, a weakly acidic ion exchanger containing the iminodiacetate group as a chelating functionality. Influence of temperature on the exchange equilibrium of these metal ions was studied in the temperature range 282–323 K. Exchange isotherms were plotted for these ions, which indicated a differential selectivity. Plots of the logarithm of selectivity coefficient and equivalent fraction of the metal ions in the exchanger phase gave the value of equilibrium constant (Ka). Based on the values of selectivity coefficient (Kc) values, selectivity of the resin for alkaline earth metal ions was in the order Sr2+>Ba2+>Ca2+>Mg2+ and for transistion metals studied the selectivity was in the order Ni2+>Cu2+>Pb2+>Mn2+>Hg2+>Fe3+>Ag+. Various thermodynamic parameters were calculated and the results indicate the preferential uptake of divalent cations over Na+ ions.

Treatment of Chloride Waste Pickle Liquor by Solvent Extraction for the Recovery of Iron

A systematic study of the extraction of Fe(III) from chloride waste pickle liquor has been investigated using Cyanex 923 diluted with kerosene to recover iron values from the pickle liquor. Various parameters were studied to optimize the conditions for maximum recovery of iron. Extraction increases with increasing concentration of both hydrochloric acid and extractant. The species extracted into the organic phase appears to be HFeCl2 with 1 M of the solvent. Effect of various salts as additives on Fe extraction was also studied and it was found that addition of NaCl enhanced the extraction about 2.5 times as compared to that without its addition. Saturated loading capacity was found to be 60.9 g/L Fe in four contacts at O/A of 1. The stripping of Fe(III) with different concentration of hydrochloric acid and nitric acid from the loaded Cyanex 923 was found to increase up to 1 M of both the acids and then decrease with further increase in acid concentration up to 10 M. However, 100% stripping efficiency of Fe(III) was achieved with 0.8 M oxalic acid in two countercurrent stages at an aqueous:organic phase ratio of 3:1. Extraction parameters for maximum extraction of Fe(III) were optimized.

Recycling of Secondary Tungsten Resources

Tungsten and its alloys find critical applications in several important sectors, such as defence, aerospace, mining, manufacturing, telecommunications etc., which are key to economic development and national security. Global tungsten deposits are limited (~3.3 million tonnes) and highly localized; China dominates the supply with more than 84% share. India doesn’t have any economic tungsten ore deposits, and produces meagre quantities of tungsten in comparison to its demand of ~1500 tonne/year. In order to lessen the import burden and supply risk to the country’s defence programmes, India is required to focus on producing this important metal from various available secondary and lean grade resources such as scraps and tailings. This article presents some of the recently developed and commercialized tungsten recycling technologies by CSIR-NML, which include: (1) recycling of tungsten carbide (WC) hard metal scraps for production of high pure yellow tungsten oxide (WO3) and W-metal powder; and (2) production of high pure sodium tungstate (Na2WO4·2H2O) from spent hydro-refining catalysts. Besides describing the process flow-sheets and product specifications, the paper highlights the advantages of CSIR-NML technologies over the presently practiced technologies.

Exploitation of Copper Bleed Stream for the Extraction and Recovery of Copper and Nickel by Bis(2,4,4-trimethylpentyl)phosphinic Acid

Bleed streams from copper electrolysis/electrowinning processes potentially contain high amounts of acid, copper, and nickel which need an effective treatment before disposal. A systematic study was carried out to optimize the parameters for the extraction and recovery of metal values using bis(2,4,4-trimethylpentyl)phosphinic acid (Cyanex 272) diluted with kerosene. Since pH has a major role to play in the separation of Cu from Ni, a 60% saponified solvent was used for extraction studies. With an increase in equilibrium pH from 3.32 to 5.48 and extractant concentration from 5 to 20%, there is an increase in the percentage extraction of metal ions. With a solvent concentration of 20%, the separation factor for Cu with respect to Ni ( ) increases from 39.1 to 118.8 with the increase in pH from 3.3 to 5.5. Loading capacity of 20% Cyanex 272 was found to be 30.8 g/L Cu and 0.024 g/L Ni. After scrubbing of coextracted Ni(II) with 15 g/L H2SO4, the loaded organic containing 30.59 g/L Cu(II) and 4 ppm Ni(II) was stripped with 75 g/L sulfuric acid. A McCabe-Thiele plot shows the requirement of two counter-current stages at an O:A ratio of 1:1 for extraction and two counter-current stages at O:A ratio of 2:1 for the stripping of copper. Results of the present investigation indicate the possibility of the use of saponified Cyanex 272 for the extraction, separation, and recovery of copper and nickel from the actual spent copper bleed streams.

Separation and Removal of Cobalt and Zinc from Chloride Solution by Indion BSR—A Chelating Resin

Abstract Ion‐exchange removal of zinc and cobalt from aqueous solutions on Indion BSR, an indigenous chelating resin, was studied in detail. The percentage removal of zinc and cobalt was examined by varying experimental conditions, viz., dosage of adsorbent, pH of the solution and contact time, metal concentration in aqueous feed, and temperature. It was found that more than 95% removal of both the metals was achieved under optimum conditions. The loading capacity for zinc and cobalt under optimized conditions was found to be 4.27 g Zn/100 g resin and 6.15 g Co/100 g resin with a feed concentration of 2 g/L each. Effect of various salts like sulfate, carbonate and chloride of sodium, and ammonium were also studied. Separation of both these metals from a binary mixture was also studied. Under optimized condition this resin was found to have more affinity for Zn than Co, indicating the feasibility of zinc separation from cobalt. The studies showed that this chelating resin could be used efficiently for the removal and separation of cobalt and zinc from chloride solutions.

Emulsion Mediated Low Temperature Pressure Leaching of Base Metals from Mixed Sulfide Minerals Through Enhanced Oxygen Mass Transfer

Total pressure oxidation (TPOX) is widely outreached leaching practice for base metals from sulfide minerals, wherein high temperature (T ~ 200 °C) and oxygen pressure (pO2 ~ 25 bar) are required. These aggressive conditions intensify the oxygen mass transfer, and therefore facilitate metal dissolution. However, challenging-cum-negative aspects of such practice are energy and material intensive requirements and high oxygen demand. Thus, the present study explores the novel emulsified medium for enhancement of oxygen mass transfer, which assists faster metal dissolution at significantly lower temperature and pressure condition. It is possible to achieve quantitative dissolution (>95%) of Cu, Ni and Co from mixed sulfide minerals at T ~ 95 °C and pO2 ~ 2 bar using an emulsion of 2.5% (v/v) n-Hexadecane in dilute sulfuric acid. In addition, n-Hexadecane was found to be inert, stable and immiscible in a pressurized leaching system, thus can be easily separated and recycled in subsequent leaching stages. Thus, this study offers an energy efficient route for low temperature-pressure leaching of sulfides.