Decomposition of monazite concentrate in sulphuric acid

A sulphuric acid bake-leach process was investigated for the extraction of rare earth elements (REEs), uranium, and thorium from a monazite concentrate. X-ray diffraction analysis showed the formation of water-soluble sulphates that readily dissolved during the water leach step. Nearly complete extraction of REEs, uranium, and thorium was achieved when the concentrate was baked at 250°C for 4?h with a sulphuric acid to concentrate (S/C) weight ratio of 4:1. At the 1:1 sulphuric acid to concentrate ratio ～65% of REEs were leached while only ～2–5% of uranium and thorium were extracted. Temperature (180–250°C) had little effect on the extraction of REEs, but greatly affected the extraction of thorium and uranium. In general, the extraction of thorium and uranium decreased with an increase in temperature. The effect of particle size (48–137?µm) was also tested and found to have little effect on the extraction of REEs. Acid consumption was calculated and found to increase with longer baking times (0.3–0.8?g acid/g concentrate). The major mineralogical phases formed because of the sulphation reaction included potassium cerium sulphate hydrate (2K₂SO₄·Ce(SO₄)₂·2H₂O), lanthanum sulphate hydrate (La₂(SO₄)₃·2H₂O), sodium praseodymium sulphite hydrate (NaPr(SO₃)₂·2H₂O), and neodymium sulphate hydrate (Nd₂(SO₄)₃·5H₂O), all of which were water-soluble.     

Empirical model for the extraction system YCl3ErCl3HClH2ODI-(2-ethylhexyl)phosphoric acid—n-heptane

Equilibrium data were obtained for the extraction of the binary rare earth mixture yttrium chloride-erbium chloride from 2 kmol/m³ HClH₂O solutions by 1 kmol/m³ di(2-ethylhexyl)phosphoric acid in n-heptane. Total rare earth concentration in the aqueous phase was 0.5 kmol/m³. It was found that yttrium concentrations in the organic phase exhibit negative deviations whereas erbium concentrations exhibit positive deviations from ideality. Empirical correlations for predicting these deviations were developed. The separation factor was calculated.     

Effect of Exogenous Zirconia Nanophases on the Structural Properties of the Sulfur- and Tin-Containing Nickel Melts

The surface tension and the density of the nickel melts with introduced ZrO₂ nanoparticles are studied by the sessile drop method using a digital camera and computer processing of images. The revealed differently directed effects of nanoparticles on the surface tension in the Ni–Sn and Ni–S systems points to a change in the structure of the melt–gas surface layer. The nanoparticles are shown to affect the adsorption of surfactants, and the surface layer is likely to consist of adsorbed Ni + (ZrO₂–surfactant) ensembles. The ZrO₂ content in a metal is determined using the technique of separate determination of the zirconium content dissolved in a metal and zirconium in the form of ZrO₂. It was found that, at 0.10 wt % ZrO₂ initially present in a metal, 0.021–0.031 wt % ZrO₂ are retained in samples; that is, about 70 rel % ZrO₂ are removed to the interface in the form of ensembles. Auger spectroscopy analysis of the Ni–Sn–ZrO₂ surface film detected 5–10 rel % Zr in the surface layer.     

Plasmachemical Processing of Rare Pefractory Metals Fluoride Solutions

Fluoride solutions are commonly used for purification and separation of rare refractory metals. Traditional technologies of oxides production from such solutions are rather complicated and ecologically not ideal. Investigations on plasmachemical processing of fluoride solutions containing niobium, tantalum, titanium and zirconium showed the possible oxides (ultrafine powder Nb_O,Ta_O, and Ti_O) and hydrofluoric acid production from these solutions^1.2)

Experiments were carried out using a MW plasmachemical plant. For plasma generation nitrogen, oxygen, and air were used. The hard product was separated on a metal net filter. Vapors condensed in a Teflon heat exchanger. In the case of titanium solution the sequence of transformations was

Drops drying and hard fluoride substance crystallization

Evaporation of fluoride titanium compounds

Hydrolysis of gaseous fluoride compounds with Ti_O production

Ti_O condensation

Gaseous processes account for production of Ti_O Nb_Oj and Ta_O oxides' ultrafine powders. If the initial titanium solutions were pure enough, Ti0₂ had good pigment characteristics. The low volatility of fluoric zirconium compounds is responsible for hard particles hydrolysis and formation of considerably large (20-100 mm) spherical hollow particles of Zr0₂. The sizes of these particles correspond to the sizes of the initial solution drops.     

Effects of precipitate aging time on the cerium-zirconium composite oxides

Cerium-zirconium composite oxides with high performance were synthesized by a co-precipitation method, using zirconium oxychloride and rare earth chloride as raw materials. The effects of precipitate aging time on the properties of cerium-zirconium composite oxides were investigated. The prepared cerium-zirconium composite oxides were characterized by X-ray diffraction（XRD）, BET specific surface area, pulsed oxygen chemical adsorption, H2 temperature-programmed-reduction（H2-TPR）, scanning electron microscopy（SEM）, etc. The results showed that the precipitate aging time caused great effects on the properties of cerium zirconium composite oxides. With the increase of aging time, the cerium zirconium composite oxides showed enhanced specific surface area, good thermal stability, and high oxygen storage capacity（OSC）. The best performance sample was obtained while the precipitate aging time up to 48 h, with the specific surface area of 140.7 m2/g, and OSC of 657.24 μmolO2/g for the fresh sample. Even after thermal aged under 1000 oC for 4 h, the aged specific surface area was 41.6 m2/g, moreover with a good OSC of 569.9 μmolO2/g.     

Diffusion Interaction during Preparation of Nanocrystalline Powders in the System ZrO2-Y2O3

The properties of ZrO₂ - 3 mole% Y₂O₃ nanocrystalline powder prepared by diffusion impregnation are studied. The original nanocrystalline powder of M-ZrO₂ is prepared with hydrothermal treatment of aqueous zirconium hydroxychloride solution by different regimes. It is found that after diffusion impregnation for all of the powders with yttrium oxide two solid solutions are formed (F-ZrO₂ and M-ZrO₂) in mixture. It is established that the morphological features typical for the original powders are retained. The efficiency of diffusion impregnation is determined by the slightly-agglomerated powder with a high degree of crystallinity.__________Translated from Poroshkovaya Metallurgiya, Nos. 3–4(442), pp. 3–11, March–April, 2005.     

电感耦合等离子体质谱法测定白云鄂博矿石中15种稀土元素总量及其分量

白云鄂博矿物为典型的晶格型矿物,含有铌、锆、钛等难溶金属的矿物,常规酸溶法处理难以将其溶解完全。采用氢氧化钠和过氧化钠碱熔融分解白云鄂博矿石样品,热水浸取,碱分离后,用盐酸和过氧化氢破坏滤纸和溶解沉淀,以1%盐酸为测定介质,通过控制基体质量浓度不大于0.5 g/L和采用Cs内标进行校正以消除基体效应,建立了电感耦合等离子体质谱法(ICP-MS)测定白云鄂博矿石中包括镧、铈、镨、钕、钐、铕、钆、铽、镝、钬、铒、铥、镱、镥、钇在内的15种稀土元素含量及其总量的方法。实验表明,各稀土元素在质量浓度为5.00~100.0 ng/mL(以氧化物计,下同)范围内和稀土元素与内标元素的强度比呈良好的线性关系,相关系数均不小于0.999 6。方法检出限为0.010~0.034 ng/mL,定量限为0.030~0.10 ng/mL。按照实验方法对白云鄂博矿石样品中稀土元素总量及其分量进行测定,测定结果与电感耦合等离子体原子发射光谱法或X射线荧光光谱法基本一致;相对标准偏差(RSD,n=6)在1.0%~4.9%之间,加标回收率在95%~105%之间。将实验方法应用于稀土矿石成分分析标准物质中稀土元素总量及其分量的测定,结果与认定值基本一致。     

电感耦合等离子体质谱法测定白云鄂博矿石中15种稀土元素总量及其分量

白云鄂博矿物为典型的晶格型矿物,含有铌、锆、钛等难溶金属的矿物,常规酸溶法处理难以将其溶解完全。采用氢氧化钠和过氧化钠碱熔融分解白云鄂博矿石样品,热水浸取,碱分离后,用盐酸和过氧化氢破坏滤纸和溶解沉淀,以1%盐酸为测定介质,通过控制基体质量浓度不大于0.5 g/L和采用Cs内标进行校正以消除基体效应,建立了电感耦合等离子体质谱法(ICP-MS)测定白云鄂博矿石中包括镧、铈、镨、钕、钐、铕、钆、铽、镝、钬、铒、铥、镱、镥、钇在内的15种稀土元素含量及其总量的方法。实验表明,各稀土元素在质量浓度为5.00~100.0 ng/mL(以氧化物计,下同)范围内和稀土元素与内标元素的强度比呈良好的线性关系,相关系数均不小于0.999 6。方法检出限为0.010~0.034 ng/mL,定量限为0.030~0.10 ng/mL。按照实验方法对白云鄂博矿石样品中稀土元素总量及其分量进行测定,测定结果与电感耦合等离子体原子发射光谱法或X射线荧光光谱法基本一致;相对标准偏差(RSD,n=6)在1.0%~4.9%之间,加标回收率在95%~105%之间。将实验方法应用于稀土矿石成分分析标准物质中稀土元素总量及其分量的测定,结果与认定值基本一致。     

Deoxidization Equilibria with Zirconium and Sulfur Partition for Molten Iron/CaO‐Al2O3‐ZrO2 Slag at 1873K

The relationship of zirconium and oxygen concentrations with sulfide capacity was clarified using equilibrated molten iron with CaO‐Al₂O₃‐ZrO₂ slag at 1873 K. Al₂O₃ and CaO‐stabilized ZrO₂ crucible saturated compositions were equilibrated with CaO‐2Al₂O₃ and crucible solid solution (Css) in the CaO‐ZrO₂ system, and with CaOZrO₂ and Css, respectively. From the concentrations of zirconium and oxygen dissolved in molten iron, ZrO₂ activities of the slag of the Al₂O₃ crucible and ZrO₂ crucible compositions were determined to be 0.885 and 0.0343, respectively. On the other hand, the sulfur distribution ratio of the ZrO₂ crucible saturated composition was higher than that of the Al₂O₃ crucible saturated composition. Sulfide capacities were determined to be 6.30×10^?5 and 8.07×10^?5 in the Al₂O₃ and the ZrO₂ crucible saturated compositions, respectively.     

Recovery of uranium,vanadium, yttrium and rare earths from phosphoric acid by a precipitation method

Commercial procedures for recovery of uranium from phosphoric acid are all based on solvent extraction techniques. Recovery of uranium from phosphoric acid in combination with direct production of concentrated acid is not possible on a commercial scale using solvent extraction. When a dispersion agent such as acetone, and a precipitation reagent - NH₄F - are added, uranium can be precipitated from high concentration (52% P₂O₅), as well as low concentration phosphoric acid (～30% P₂O₅) with 0.6 kg acetone/kg P₂O₅ and 60 g NH₄F/kg P₂O₅. Variation of all parameters, such as uranium valence, phosphoric acid concentration, type and quantity of the dispersion and precipitation agents, has made it possible to develop on a laboratory scale a preferential mode of operation which appears to make uranium recovery from high concentration acid even simpler than recovery from acid of low concentration. This method also enables recovery of ?90% of the yttrium and ?80% of the rare earths contained in the phosphoric acid. To precipitate vanadium much more acetone must be used. The economic calculations presented here show that uranium recovery by the precipitation method is considerably less expensive than recovery by extraction or by other proposed routes: $60/lb at phosphoric acid capacity of 300 kt/a P₂O₅ with solvent extraction and $41/lb yellow cake with the new precipitation route and the same capacity. At present uranium prices ($28/lb yellow cake), the precipitation method does not make uranium recovery by precipitation an economic proposition in the case of plants of moderate phosphoric acid capacities (about 300 kt/a P₂O₅); however, in combination with recovery of yttrium and/or rare earths it appears to become economic - $28/lb yellow cake - at this moderate capacity.     

Processing of xenotime concentrate

Xenotime is a rare earth phosphate mineral which is a rich source of yttrium and heavy rare earths. Earlier experimental studies have been carried out in this laboratory on the chemical processing of hand-sorted xenotime obtained from the Bihar region to rare earth oxide intermediates. In addition to the deposits of xenotime in the Bihar region there are large volumes of placer deposits of rare earths containing both monazite and xenotime in the Siri river basin of Madhya Pradesh. Atomic Minerals Division is operating a pilot plant for the beneficiation of rare earths from these Siri river deposits. A low grade (typically analysing 45% light rare earth oxide, 3.4% Y₂O₃ and 2.3% heavy rare earth oxide) and intermediate grade (analysing 18.5% light rare earth oxide, 19.3% Y₂O₃ and 8.7% heavy rare earth oxide) concentrate is routinely being produced. The paper reports experimental studies involving alkali leaching and alkali fusion studies to recover rare earth oxide intermediates from low and intermediate grade deposits from Madhya Pradesh. It has been shown possible to extract almost 95% of rare earths by these processes.     

Preparation of technical zirconium diboride by the carbothermic reduction of mixtures of zirconium and boron oxides

Conclusions A study was made of the preparation of technical zirconium diboride by the reduction of mixtures of zirconium and boron oxides with carbon under industrial conditions. It is shown that the optimum conditions for the preparation of zirconium diboride by the carbothermic method are established when a charge having the composition ZrO₂+1.2 B₂O₃+5 C (i.e., with a 20% excess of boric anhydride over the stoichiometric composition) is reduced at 2000°C in a hydrogen or converted gas atmosphere. The resultant ZrB₂ contains 18–19% B (compared with the theoretical boron content of 19.25%) and not more than 0.8% C.Translated from Poroshkovaya Metallurgiya, No. 11 (131), pp. 80–84, November, 1973.     

Preparation of crystalline mixed rare earth carbonates by Mg(HCO_3)_2 precipitation method

In acid treatment technology of Baotou mixed rare earth ore,large quantities of ammonia-nitrogen wastewater are produced in the step of ammonium bicarbonate precipitation to transform rare earth sulfate.In this paper,we adopted a green precipitant magnesium bicarbonate(Mg(HCO_3)_2) to substitute ammonium bicarbonate to eliminate ammonia-nitrogen pollution.The effects of n(HCO_3~-):n(RE~(3+)),aging temperature and aging time on the crystallization using Mg(HCO_3)_2 precipitation method were investigated.The results indicate that the rare earths could be completely recovered when n(HCO_3~-):n(RE~(3+)) is higher than 3.15:1.The crystal water content of rare earth carbonates is affected by the aging temperature.The precipitate has a bad filterability when the aging temperature is over 40℃.This can be attributed to the less crystallized water molecules of the hydrated rare earth carbonate precipitation.The mixed rare earth carbonates are prone to be crystalline,and have a good filterability at aging temperatures below 40℃.Meanwhile,the evolution mechanism of crystalline mixed rare earth carbonates is reasonably deduced,the amorphous rare earth carbonates are first dissolute and then recrystallized.Under the optimized aging conditions,the purity of the crystalline precipitate meets the requirements of the fine product standard(GB/T 16479-2008).The filtrated could be used to produce Mg(HCO_3)_2,thus to realize the recycling of magnesium sulfate.     

Recovery of yttrium from deep-sea mud

Deep-sea mud rich in rare earth yttrium has received lots of attention from the international community as a new resource for Y. A novel process, which mainly includes acid leaching, solvent extraction, and oxalic acid precipitation-roasting, is proposed for recovery of Y from deep-sea mud. A series of experiments were conducted to inspect the impacts of various factors during the process and the optimum conditions were determined. The results show that the Y of deep-sea mud totally exists in apatite minerals which can be decomposed by hydrochloric acid and sulfuric acid solution. The highest leaching efficiency of Y is 94.53% using hydrochloric acid and 84.38% using sulfuric acid under the conditions of H~+concentration 2.0 mol/L, leaching time 60 min, liquid-solid ratio 4:1 and room temperature 25 ℃(only in case of sulfuric acid, when using hydrochloric acid, the leaching temperature should be 60 ℃). Because of the much lower leaching temperature, sulfuric acid leaching is preferred. The counter current extraction and stripping tests were simulated by a cascade centrifugal extraction tank device. Using 10 vol% P204,15 vol% TBP and 75 vol% sulfonated kerosene as extractant, 98.79% Y~(3+) and 42.60% Fe~(3+) are extracted from sulfuric acid leaching liquor(adjusted to pH = 2.0) after seven-stage counter current extraction with O/A ratio of 1:1 at room temperature, while other metals ions such as Al~(3+), Ca~(2+), Mg~(2+)and Mn~(2+) are almost not extracted. The Y~(3+) in loaded organic can be selectively stripped using 50 g/L sulfuric acid solution and the stripping efficiency reaches 99.86% after seven-stage counter current stripping with O/A ratio of 10:1 at room temperature, while only 2.26% co-extracted Fe~(3+) is stripped. The Y~(3+) of loaded strip liquor can be precipitated by oxalic acid to further separate Y~(3+) and Fe~(3+). The precipitation efficiency of Y~(3+) in loaded strip liquor can be 98.56% while Fe~(3+) is not precipitated under the conditions of oxalic acid solution concentration 200 g/L, quality ratio of oxalic acid to Y of 2, and precipitation time 0.5 h. And the precipitate was roasted at 850 ℃ for 3 h to obtain the oxide of Y in which the purity of Y_2 O_3/REO is 79.02% and the contents of major non-rare earth impurities are less than 0.21%.Over the whole process included acid leaching, solvent extraction, and oxalic acid precipitation-roasting,the yttrium yield is 82.04%.     

Pyrite oxidation with ozone: stoichiometry and kinetics

One of the most frequent causes of refractoriness in precious metals leaching is their occlusion or fine dissemination into a pyritic matrix. This study experimentally explores the acid leaching of pyrite with ozone, suggests the stoichiometry of the reaction, estimates its activation energy and defines the effect of the main variables on the leaching kinetics. The results of stoichiometry tests allow establishing that one mole of pyrite requires 7.7 moles of ozone to produce one mole of ferric ion and 2 moles of HSO₄? ions. A decrease in the particle size, solution pH and solids’ concentration of the leaching system increases pyrite dissolution. The type of acid (nitric, sulphuric and hydrochloric) does not affect pyrite dissolution rate. Up to 60% of pyrite is dissolved when the optimal experimental conditions are employed (1?g pyrite (?25?µm), 800?mL of 0.18?M of H₂SO₄, 800?rev?min^?1, 1.2?L?min^?1 gas stream O₂/O₃ with 0.079?g O₃?L^?1 and 25°C). The apparent activation energy of the pyrite-ozone reaction is 14.92?kJ?mol^?1, and the absence of a passive layer on the pyrite surface and the linearity of the dissolution profiles suggest that the dissolution kinetics is controlled by the chemical reaction.     

EDTA滴定法测定稀土铝中间合金中稀土总量

准确测定稀土铝中间合金中稀土总量,对于有效控制稀土铝中间合金的生产技术和产品质量具有重要意义。用400g/L氢氧化钠溶液溶解试样,此时,稀土与氢氧化钠反应生成氢氧化稀土沉淀,而铝与氢氧化钠反应后以偏铝酸根的形式留在了试液中,过滤,实现了铝与稀土元素的分离;用盐酸溶解沉淀,加入氢氟酸,此时稀土和氢氟酸反应生成氟化稀土沉淀,而铁与氢氟酸反应形成络合物留在溶液中,过滤,实现了干扰元素铁与稀土元素的分离;加入盐酸和高氯酸溶解沉淀,用抗坏血酸还原残留铁(III),乙酰丙酮溶液掩蔽残留的少量干扰元素铝,控制pH 5.5,以二甲酚橙作指示剂,用EDTA标准溶液滴定至溶液由红紫色变为亮黄色即为终点,建立了EDTA滴定法测定稀土铝中间合金中稀土总量的方法。将实验方法用于稀土铝中间合金(镧铝、钐铝、铒铝、钇铝)试样中稀土总量的测定,并在试样中分别加入不同量的于950℃马弗炉中灼烧过的高纯氧化镧、高纯氧化钐、高纯氧化铒和高纯氧化钇试剂进行加标回收试验,结果的相对标准偏差(RSD,n=11)不大于0.30%,加标回收率为99.6%~100.4%。选取镧铝、钐铝试样,按照实验方法测定其中稀土总量,并采用国标GB/T 31966—2015中的草酸盐重量法进行方法比对试验,测定结果基本一致。     

Effects of stabilization of ZrO2 by REM oxides in Al2O3-ZrO2 compositions

Conclusions Melting and high-rate quenching the melt of the Al₂O₃-ZrO₂-REM oxide melt results in the formation of a heterogeneous material with a highly homogenized structure in which the oxides/ stabilizers are completely dissolved in ZrO₂. Mechanical dispersion (vibrogrinding) of the granules and subsequent heat treatment of the specimens compacted from these powders lead to partial destabilization of the solid solutions based on ZrO₂. An exception is represented by the (Al₂O₃-ZrO₂)-Y₂O₃ and (Al₂O₃-ZrO₂)-Sc₂O₃ compositions. High temperature cause recrystallization growth of structural components and coarsening of the eutectic structure of all compositions. The highest stability was recorded for the composition in which ZrO₂ is stabilized by the yttrium oxides.Translated from Poroshkovaya Metallurgiya, No. 11(323) pp. 52–55, November, 1989.     

Extraction and separation of yttrium from other rare earths in chloride medium by phosphorylcarboxylic acids

Two phosphorylcarboxylic acids, 3-((bis(2-ethylhexyloxy))phosphoryl)propanoic acid (PPA) and 3-((bis(2-ethylhexyloxy))phosphoryl)-3-phenylpropanoic acid (PPPA), were synthesized for separating yttrium from other rare earths in the chloride feed of ion-adsorption type rare earth concentrate. The effect of the factors such as pH_1/2, temperature, saponification degree and phase modifiers was investigated. The separation efficiencies of PPA and PPPA are obviously better than the typical extractants such as sec-octylphenoxy acetic acid (CA-12) and naphthenic acid (NA). The extraction process of rare earths by PPA and PPPA is a cation exchanging reaction, which is similar to those of CA-12 and NA. The loaded rare earths in both PPA and PPPA systems can be effectively back-extracted by 0.5 mol/L HCl or higher concentration. A cascade extraction process for separating yttrium from other rare earths was developed using PPPA as the extractant. The yttrium product with the purity of 97.20 wt% was obtained by 35 stages of extraction and 12 stages of scrubbing.     

MnO2 reduction by calcium lignosulfonate: the kinetics and mechanism studies

ABSTRACT

The kinetics and mechanism of the reduction of manganese dioxide ore by calcium lignosulfonate (CLS) in acid solution were investigated. The results showed that the reducing process mainly occurred after the adsorption and then decomposition of CLS by ore and the concentration of sulphuric acid exerted an enhancing effect on both CLS adsorption and manganese extraction. The effects of leaching temperature, the mass ratio of CLS to MnO₂ in ore, concentration of sulphuric acid as well as leaching time on per cent leached of Mn were also discussed. The experimental data were well interpreted with a shrinking core model of internal diffusion, and an overall kinetic model was established. The reaction rate constant was found to be proportional to the mass ratio of CLS to MnO₂ in ore and concentration of sulphuric acid, and the apparent activation energy was determined to be 69.4?kJ?mol^?1 by using Arrhenius expression.     

The concentration of rhodium and iridium during the final stages of the platinum group metals refining process using the co-polymer poly[(N-dithiocarboxylato)-iminoethenehydrogenoiminioethene]

This investigation examines the use of the insoluble co-polymer poly[(N-dithiocarboxylato)iminoethenehydrogenoiminoethene] (PIED) as an extractant for rhodium and iridium towards the end of the platinum group metals refining process (e.g., after solvent extraction of Au, Pd and Pt). The results indicate that the co-polymer is surprisingly stable in hydrochloric acid (5 molar) and that good extractions of rhodium and iridium can be achieved (99.9%). The polymer has a high capacity for both rhodium and iridium which form complexes with the —NCS₂H groups appended to the polymer, and the rates of uptake of rhodium and iridium on the polymer are acceptable ($\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ for Rh and Ir ca. 5 min). The metal-polymer complexes have also proved to be easy to decompose by chemical treatment, e.g., with hydrogen peroxide. The chemical treatment with a mixture of hydrogen peroxide and sulphuric acid is the preferred route, as separation of concentrated solutions of rhodium(III) and iridium(IV) sulphates is then possible using established procedures. The main application of this co-polymer could be in values recovery as it appears to have little selectivity.