Archana Agrawal

An overview on the production of pigment grade titania from titania-rich slag

To recover pigment grade TiO2, operating plants all over the world use chemical processes. Slag-based technology is considered to be attractive because of low waste generation and low chemical cost due to high titanium content and is poised to replace the conventional technology. This paper provides a review of the slag-based technology with the specific aim to produce leachable slag and achieving high titania yield from recovered wastes. Leachable oxides of the lower oxidation state, such as TiO and Ti2O3, facilitate the leaching process. However, during smelting these oxides increase the viscosity of the slag. Formation of titanium carbide or carbonitride is also not desirable as it leads to resistance to the leaching of titanium. This report highlights the problems and their possible solutions to obtain leachable slag.

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.

Recent trends and current practices for secondary processing of zinc and lead. Part I: lead recovery from secondary sources.

Implementation of stricter environmental laws and economic reasons has forced all the metallurgical industries to go for eco-friendly technologies to produce metal and other related products. However, generation of wastes is an integral part of metallurgical industries. If the wastes/residues are hazardous in nature, they generally have to be treated or/and disposed of in safe and designated dumping sites. If these wastes/residues are non-hazardous in nature, then they may be suitable for use as secondary raw material to recover metals such as lead, copper etc., which are in growing demand all over the world. The processing of lead secondaries is important because of their relative high metal content, as well as the low energy and cost involved in recovering the metal. This paper mainly focuses on the current practices and recent trends in the secondary processing of lead. Various processes, particularly hydrometallurgical ones, already developed or in the development stages, are discussed. Attempts made by various Council of Scientific and Industrial Research (CSIR) Laboratories including the National Metallurgical Laboratory (NML) and industries such as Binani Zinc to develop eco-friendly processes for the recovery of lead from secondary raw materials are also described.

Adsorption Kinetics for the Removal of Co(II) and Zn(II) from Wastewater by Indion BSR — A Chelating Ion-Exchange Resin

A comparative study on the adsorption of zinc(II) and cobalt(II) from aqueous solutions onto Indion BSR, an indigenous cation-exchange resin, was undertaken in the present work. Various parameters for the removal of Co(II) and Zn(II) such as the initial solution pH, contact time, resin and metal ion concentration were optimized. The equilibrium data obtained were well fitted by both the Langmuir adsorption isotherm at pH 6.0 for 500 mg resin and the Freundlich adsorption isotherm under optimum conditions of contact time and pH 5.0 for 250 mg resin at 30°C. The adsorption of Zn(II) and Co(II) on this cation-exchange resin followed first-order reaction kinetics. Film diffusion of Co(II) and Zn(II) in this ion-exchange resin was shown to be the main rate-limiting step over the concentration range studied. The studies showed that the resin could be used as an efficient adsorbent for the removal of Co(II) and Zn(II) from aqueous solutions.

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.

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.

Process integration for material synthesis from a deactivated catalyst: Studies on the interaction of metal ions between two immiscible phases

Present investigation deals with the treatment of deactivated Co-Mn bromide catalyst for the recovery of Co and Mn as Co metal powder and chemical manganese dioxide by an integrated process comprising of a selective metal ion transfer from an aqueous solution containing a mixture of metal ions with a saponified solution of di-2ethyl-hexyl phosphoric acid, followed by selective scrubbing and metal stripping. The pure metal solutions so obtained were subjected to precipitation and hydrothermal treatment to obtain a desired material. The deactivated catalyst was leached by H2SO4 in presence of H2O2 followed by removing Fe, Si etc. The purified leach liquor of composition: 6.9g/L Co, 9.4g/L Mn was used for detail study to optimize the best conditions for the separation of Co from Mn. Experimental observations show that the extraction of both increased with increasing equilibrium pH and the concentration of the organic, with a separation factor of about 10, at equilibrium pH of 3. A quantitative extraction of Mn was possible with 20% D2EHPA in three stage counter-current extraction. After Co scrubbing, Mn was stripped with dilute H2SO4 and high pure spherical shaped CMD was produced. Co in the raffinate was recovered as powder by hydrothermal H2- reduction.

Selective Production of Co and Ni Powders Through Hydrothermal Reduction of Leach Solutions of a Synthetic Matte Containing Cu-Ni-Co-Fe-S

Synthesis of metal powders with tailored characteristics, such as those of Cu, Ni & Co has been the subject of much attention during the past decades. This is due to their potential technological applications in several critical & emerging areas, e.g. in the manufacturing of energy storing devices, optoelectronic and magnetic recording media, high end catalysts, etc. etc. In recent years, nano particles of nickel have found applications as electrodes in multi layer ceramic capacitors (MLCC) due to their excellent electrical conductivity, high melting temperature & low cost [1–3]. Similarly, fine cobalt powders are one of the main constituent for manufacture of rare-earth based permanent magnets [4].