Application of Eh-pH Diagrams on Acid Leaching Systems for the Recovery of REEs from Bastnaesite, Monazite and Xenotime

Bastnaesite, monazite and xenotime are rare earth minerals (REMs) that are typical sources for rare earth elements (REEs). To advance the understanding of their leaching and precipitation behavior in different hydrometallurgical processes, Eh-pH diagrams were constructed and modified using the HSC 9.9 software. The aqueous stability of rare earth elements in H2O and acid leaching systems, i.e., the REE-Ligands-H2O systems, were depicted and studied based on the Eh-pH diagrams. This study considers the most relevant lixiviants, their resulting equilibrium states and the importance in the hydrometallurgical recovery of rare earth elements (REMs). A literature review was performed summarizing relevant Eh-pH diagrams and associated thermodynamic data. Shifting stability regions for REEs were discovered with additions of acid ligands and a narrow stability region for soluble REE-(SO4/Cl/NO3) complexes under highly acidic conditions. As such, the recovery of REEs can be enhanced by adjusting pH and Eh values. In addition, the Eh-pH diagrams of the major contaminants (i.e., Fe, Ca and Al) in leaching systems were studied. The resulting Eh-pH diagrams provide possible insights into potential passivation on the particle surfaces due to the formation of an insoluble product layer.

A review of Kurozu, amber rice vinegar made in pottery jars

Brewed rice vinegar, Kurozu, is a traditional Japanese vinegar with a dark amber color. Kurozu is produced in a regional area of Japan using traditional techniques and made inside handcrafted pottery jars. Kurozu is used as both a seasoning and a healthcare supplement. In vitro and in vivo investigations of ingredients in Kurozu have been carried out. Studies of the functional aspects of Kurozu began in the 1980s, and the health promoting and disease preventing effects of Kurozu have since been elucidated. It was reported that Kurozu improved the symptoms of hypertension, allergies, hypercholesterolemia, enhanced carbohydrate metabolism, and inhibited tumor growth. Kurozu-Moromi is an insoluble product created from the fermentation of Kurozu. Kurozu-Moromi also shows valuable properties, including improvement in dyslipidemia, prevention of hyperglycemia, antitumor effect, and antiallergic activity.Keywords: Amber color, Brewed vinegar, Functionality, Moromi, Pottery jars

Study of Thermal Reduction of Barium Sulphate for Barium Sulphide Preparation

Industrial wastewaters, particularly those associated with mining and mineral processing, can contain high con-centrations of sulphate. There are various methods of sulphate removal e.g. reverse osmosis, ion exchange, precipitation by lime, cements, and salts of barium and the biological removal process. The soluble salts of barium are most commonly used for precipitation of sulphate from aquatic acidic solutions to the insoluble product barium sulphate BaSO4. Benefits of precip-itation are high sulphate removal efficiency but limitations are toxicity of barium compounds and high economical costs. For this reason the recycling of BaSO4 to barium sulphide BaS (the precipitating reagent) is very important. The paper deals with study of BaSO4 reduction by activated carbon to BaS by thermal analysis and infrared spectrometry. DCS analysis indicated that conversion of BaSO4 to BaS in the range of temperature 800–1,000 °C was performed. Thermal analysis and infrared spectra of the products confirmed the change in its composition, but process of reduction by carbon was incomplete and in sample was still present a part of BaSO4. Presence of BaS was confirmed by colorimetric method.

Treatment of alumina refinery waste (red mud) through neutralization techniques: A review

In the Bayer process of extraction of alumina from bauxite, the insoluble product generated after bauxite digestion with sodium hydroxide at elevated temperature and pressure is known as ‘red mud’ or ‘bauxite residue’. This alumina refinery waste is highly alkaline in nature with a pH of 10.5–12.5 and is conventionally disposed of in mostly clay-lined land-based impoundments. The alkaline constituents in the red mud impose severe and alarming environmental problems, such as soil and air pollution. Keeping in view sustainable re-vegetation and residue management, neutralization/treatment of red mud using different techniques is the only alternative to make the bauxite residue environmentally benign. Hence, neutralization techniques, such as using mineral acids, acidic waste (pickling liquor waste), coal dust, superphosphate and gypsum as amenders, CO2, sintering with silicate material and seawater for treatment of red mud have been studied in detail. This paper is based upon and emphasizes the experimental work carried out for all the neutralization techniques along with a comprehensive review of each of the processes. The scope, applicability, limitations and feasibility of these processes have been compared exhaustively. Merits and demerits have been discussed using flow diagrams. All the techniques described are technically feasible, wherein findings obtained with seawater neutralization can be set as a benchmark for future work. Further studies should be focused on exploring the economical viability of these processes for better waste management and disposal of red mud.

Detection of hydrogen peroxide and glucose by enzyme product precipitation on sensor surface

Biocatalysed precipitation of an insoluble product accumulated on the enzyme-modified electrode surface was applied as the amplification path for low concentration sensing of hydrogen peroxide and glucose. Sensitive electrochemical and quartz-crystal microbalance (QCM) biosensors based on biocatalytic precipitation were developed. A horseradish peroxidase (HRP) monolayer-modified electrode was used to sense H

Nucleation Controlled Growth of Cadmium Oxalate Crystals in Agar Gel and Their Characterization

Perfect single crystals of cadmium oxalate have been grown using the slow and controlled reaction between cadmium acetate and oxalic acid in agar gel media at ambient temperature, resulting in the formation of insoluble product Cd(COO)2. Different methods for growing crystals were adopted. The optimum conditions were employed in each method by varying the concentration of gel and reactants, gel setting time, and so forth. Prismatic, transparent single crystal about 20 times larger than the crystals obtained in various other methods at the interstitial by adding impurities in the gel was obtained. The grown crystals was characterized with the help of FT-IR studies and triclinic system of crystals were supported with lattice parameters a = 8.803 A0, b = 22.352 A0, c = 5.706 A0, α = 95.74 A0, β = 90.92 A0, γ = 117.01 A0, and V = 994.69 A03, calculated from X-ray diffractogram.

A Novel Signal-Amplified Immunoassay for the Detection of C-Reactive Protein Using HRP-Doped Magnetic Nanoparticles as Labels with the Electrochemical Quartz Crystal Microbalance as a Detector

A novel horseradish peroxidase- (HPR-) doped magnetic core-shell Fe3O4@SiO2@Au nanocomposites (Fe-Au MNPs) were employed on immunoassay for the determination of C-reactive protein (CRP) based on a electrochemical quartz crystal microbalance detector (EQCM). Firstly, the secondary CRP antibody and HRP were both immobilized on the Fe-Au MNPs (Fe-Au MNPs-anti-CRP2/HRP) as a signal tag. Secondly, the above tag and the primary antibody (anti-CRP1) in the bottom of 96-well microtiter plate were employed to conjugate with a serial of CRP concentrations to produce a sandwich immunocomplex. Thirdly, the immunocomplex solution was subsequently exposed to3,3′-diaminobenzidine (DAB) in the presence of H2O2, resulting in an insoluble product. When the precipitation solution was dripped on EQCM, it can achieve a decrease of frequency of crystal (Δf). The amount ofΔfwas proportional to (CRP) from 0.003 to 200 ng mL−1with a low detection limit of 1 pg mL−1. Compared with the enzyme-linked immunosorbent assay (ELISA), the immunoassay shows greatly improved sensitivity due to the significant amount of HRP labeled on signal tag. It also has good specificity and low sample consumption, which is expected to be a benefit for the CRP screening in early diagnosis of cardiovascular disease.