Rubidium jarosite and thallium jarosite — new synthetic jarosite-type compounds and their structures

Rubidium jarosite (RbFe₃(SO₄)₂(OH)₆) and thallium jarosite (TlFe₃(SO₄)₂(OH)₆) were synthesized as single phase products by precipitation from aqueous solution. Hydronium ion (H₃O⁺) substitutes for part of the “alkali” metal in these compounds. Both jarosites are hexagonal (R3m) and have similar unit cell dimensions. During heating rubidium jarosite undergoes two major decompositions; initially water is evolved and subsequently sulphur oxides are emitted. Thallium jarosite decomposes in three principal stages during programmed heating. The first two stages are similar to the decomposition of rubidium jarosite; the third decomposition involves the breakdown of thallium sulphate and the subsequent sublimation of thallous oxide.     

Factors affecting alkali jarosite precipitation

Several factors affecting the precipitation of the alkali jarosites (sodium jarosite, potassium jarosite, rubidium jarosite, and ammonium jarosite) have been studied systematically using sodium jarosite as the model. The pH of the reacting solution exercises a major influence on the amount of jarosite formed, but has little effect on the composition of the washed product. Higher temperatures significantly increase the yield and slightly raise the alkali content of the jarosites. The yield and alkali content both increase greatly with the alkali concentration to about twice the stoichiometric requirement but, thereafter, remain nearly constant. At 97 °C, the amount of product increases with longer retention times to about 15 hours, but more prolonged reaction times are without significant effect on the amount or composition of the jarosite. Factors such as the presence of seed or ionic strength have little effect on the yield or jarosite composition. The amount of precipitate augments directly as the iron concentration of the solution increases, but the product composition is nearly independent of this variable. A significant degree of agitation is necessary to suspend the product and to prevent the jarosite from coating the apparatus with correspondingly small yields. Once the product is adequately suspended, however, further agitation is without significant effect. The partitioning of alkali ions during jarosite precipitation was ascertained for K:Na, Na:NH₄, K:NH₄, and K:Rb. Potassium jarosite is the most stable of the alkali jarosites and the stability falls systematically for lighter or heavier congeners; ammonium jarosite is slightly more stable than the sodium analogue. Complete solid solubility among the various alkali jarosite-type compounds was established.     

The behavior of thallium during jarosite precipitation

Jarosite precipitation provides an effective means of eliminating thallium from zinc processing circuits, and a systematic study of the extent and mechanism of thallium removal during the precipitation of ammonium, sodium, and potassium jarosites was carried out. Thallium (as Tl⁺) substitutes for the “alkali” ion in the jarosite structure. Nearly ideal jarosite solid solutions are formed with potassium, but thallium is preferentially precipitated relative to either ammonium or sodium. Approximately 80 pct of the dissolved thallium precipitates during the formation of ammonium jarosite; the extent of thallium removal is virtually independent of thallium concentrations in the 0 to 3000 mg/L Tl range and of the presence of 75 g/L of dissolved Zn. Although the deportment of thallium is nearly independent of (NH₄)₂SO₄ or Na₂SO₄ concentrations >0.1 M, the precipitates made from more dilute media are relatively enriched in thallium. Likewise, the precipitates made from dilute ferric ion media are also Tl-rich. Low solution pH values or low temperatures both significantly reduce the amount of jarosite formed, but the precipitates made under these conditions are enriched in thallium. Furthermore, because thallium jarosite is more stable than the ammonium or sodium analogues, the initially formed precipitates are consistently Tl rich. The presence of jarosite seed accelerates the precipitation reaction, but dilutes the thallium content of the product. The results suggest that most of the thallium in a hydrometallurgical zinc circuit could be selectively precipitated in a small amount of jarosite, by carrying out the precipitation reaction for a short time in the absence of seed and from solutions having low alkali concentrations.     

Kinetic model for the cyanidation of silver ammonium jarosite in NaOH medium

A synthesis of silver ammonium jarosite has been carried out obtaining a single-phase product with the formula: [(NH₄)_0.71(H₃O)_0.25Ag_0.040]Fe_2.85(SO₄)₂(OH)_5.50. The product consists on compact spherical aggregates of rhombohedral crystals. The nature and kinetics of alkaline decomposition and also of cyanidation have been determined. In both processes an induction period followed by a conversion period have been observed. During decomposition, the inverse of the induction period is proportional to [OH⁻]^0.75 and an apparent activation energy of 80 kJ mol^− 1 was obtained; during the conversion period, the process is of 0.6 order (OH⁻ concentration) and an activation energy of 60 kJ mol^− 1 was obtained. During cyanidation, the inverse of the induction period is proportional to [CN⁻]^0.5 and an apparent activation energy of 54 kJ mol^− 1 was obtained; during the conversion period the process is of 0 order (CN⁻ concentration) and an activation energy of 52 kJ mol^− 1 was obtained. Results obtained are consistent with the spherical particle model with decreasing core and chemical control, in the experimental conditions employed. For both processes and in the basis of the behaviour described, two mathematical models, including the induction and conversion periods, were established, that fits well with the experimental results obtained. Cyanidation rate of different jarosite materials in NaOH media have also been established: this reaction rate at 50 °C is very high for potassium jarosite, high and similar for argentojarosite and ammonium jarosite, lower for industrial ammonium jarosite and negligible for natural arsenical potassium jarosite and beudantite. These results confirm that the reaction rate of cyanidation decreases when the substitution level in the jarosite lattice increases.     

Factors affecting lead jarosite formation

The importance of lead jarosite in hydrometallurgical processing and the factors affecting its formation in both the slow addition and autoclave synthesis techniques are discussed. In the slow addition method the principal factors are the amount and rate of delivery of soluble lead to the hot ferric sulphate solution; high temperatures and good agitation are also essential to avoid the formation of PbSO₄. The key step in the autoclave synthesis process is the selective removal of residual PbSO⁴ from the reaction product and methods of accomplishing this are described. The major factors affecting the autoclave synthesis of lead jarosite are the ratio of $\text{PbSO}{}_4\text{Fe}{}^{\mathrm{3+}}$, acid concentration and the ionic strength of the solution. Time, temperature, degree of agitation and seeding all affect the reaction but to a lesser degree. The principal techniques identified to suppress lead jarosite formation were high acidity (> 0.3 M H₂SO₄ or the presence of substantial quantities (> 0.3 M) of other jarosite formers such as K₂SO₄. Lead jarosites containing more than 16% Pb were produced and X-ray diffraction data for such material are presented.     

Synthesis, Thermodynamic, and Kinetics of Rubidium Jarosite Decomposition in Calcium Hydroxide Solutions

Rubidium jarosite was synthesized as a single phase by precipitation from aqueous solution. X-ray diffraction and scanning electron microscopy energy-dispersive spectrometry analysis showed that the synthetic product is a solid rubidium jarosite phase formed in spherical particles with an average particle size of about 35???m. The chemical analysis showed an approximate formula of Rb_0.9432Fe₃(SO₄)_2.1245(OH)₆. The decomposition of jarosite in terms of solution pH was thermodynamically modeled using FACTSage by constructing the potential pH diagram at 298?K (25?°C). The E-pH diagram showed that the decomposition of jarosite leads to a goethite compound (FeO·OH) together with Rb⁺ and $ {\text{SO}}_{4}^{2 - } $ ions. The experimental Rb-jarosite decomposition was carried out in alkaline solutions with five different Ca(OH)₂ concentrations. The decomposition process showed a so-called ??induction period?? followed by a progressive conversion period where Rb⁺ and $ {\text{SO}}_{4}^{2 - } $ ions formed in the aqueous solutions, whereas calcium was incorporated in the solid residue and iron gave way to goethite. The kinetic analysis showed that this process can be represented by the shrinking core chemically controlled model with a reaction order with respect to Ca(OH)₂ equals 0.4342 and the calculated activation energy is 98.70?kJ mol^?C1.     

Kinetics of Alkaline Decomposition and Cyaniding of Argentian Rubidium Jarosite in NaOH Medium

The alkaline decomposition of Argentian rubidium jarosite in NaOH media is characterized by an induction period and a progressive conversion period in which the sulfate and rubidium ions pass to the solution, leaving an amorphous iron hydroxide residue. The process is chemically controlled and the order of reaction with respect to hydroxide concentration in the range of 1.75 and 20.4?mol OH^? m^?3 is 0.94, while activation energy in the range of temperatures of 298?K to 328?K (25?°C to 55?°C) is 91.3?kJ mol^?1. Cyaniding of Argentian rubidium jarosite in NaOH media presents a reaction order of 0 with respect to NaCN concentration (in the range of 5 to 41?mol m^?3) and an order of reaction of 0.62 with respect to hydroxide concentration, in the range of 1.1 and 30?mol [OH^?] m^?3. In this case, the cyaniding process can be described, as in other jarosites, as the following two-step process: (1) a step (slow) of alkaline decomposition that controls the overall process followed by (2) a fast step of silver complexation. The activation energy during cyaniding in the range of temperatures of 298?K to 333?K (25?°C to 60?°C) is 43.5?kJ mol^?1, which is characteristic of a process controlled by chemical reaction. These results are quite similar to that observed for several synthetic jarosites and that precipitated in a zinc hydrometallurgical plant (Industrial Minera México, San Luis Potosi).     

Factors affecting the precipitation of chromium(III) in jarosite-type compounds

Jarosite precipitation is a useful means of stabilizing toxic species, and accordingly, the factors affecting the precipitation of chromium(III) in jarosite-type compounds was systematically investigated in a series of laboratory experiments. Although end-member Cr(III) analogues of jarosite-type compounds could not be precipitated at temperatures <100 °C, several percent Cr(III) substitution for Fe(III) in potassium jarosite and sodium jarosite was observed. However, at temperatures >200 °C, the Cr(III) analogue of potassium jarosite (KCr₃(SO₄)₂(OH)₆) is readily precipitated. The Cr(III) analogue has the R $\bar 3$ m structure characteristic of jarosite-type compounds, with a=7.23±0.02Å and c=17.02±0.02 Å. The well-crystallized material typically contains (wt pct): ～7K, ～25Cr, and ～41SO₄. The composition suggests the partial substitution of hydronium ion for potassium and some chromium vacancies in the structure. The formation of the Cr(III) analogue is promoted by increasing temperatures, retention times, and Cr(III) concentrations. Increasing acid concentrations reduce the amount of product formed but suppress the undesirable precipitation of amorphous phases. Although increasing K₂SO₄ concentrations result in a greater mass of precipitate, the products formed from concentrated K₂SO₄ solutions are contaminated with an amorphous phase. In fact, the overall results suggest that an amorphous phase precipitates initially and that the Cr(III) analogue of potassium jarosite forms by the recrystallization, or the dissolution-reprecipitation, of the amorphous phase.     

The co-precipitation of copper and zinc with lead jarosite

The formation of lead jarosite, Pb_0.5Fe₃(SO₄)₂(OH)₆, in the presence of dissolved copper and/or zinc results in a significant substitution of these metals in the jarosite phase; the co-precipitation is most pronounced in sulphate media but also occurs, to a lesser degree, in chloride solutions. The copper and/or zinc substitute for iron, and under extreme conditions the product approaches beaverite, Pb(Cu,Zn)Fe₂(SO₄)₂(OH)₆, in structure and composition. The extent of co-precipitation increases sharply with increasing concentrations of dissolved CuSO₄ or ZnSO₄ and slightly with either an increasing stoichiometric ratio of PbSO₄/Fe³⁺ or increasing ionic strength. The co-precipitation of copper or zinc is not significantly affected by acid concentration although the yield of product declines with increasing concentration of H₂SO₄. The extent of reaction is relatively insensitive to reaction temperatures in the range 130–180°C and to reaction times in excess of 2 h. Copper is strongly co-precipitated in preference to zinc from solutions containing both metals. Other divalent base metals such as Co, Ni and Mn are also co-precipitated with lead jarosite although not to the same degree as copper or zinc.     

Characterization and alkaline decomposition/cyanidation of beudantite–jarosite materials from Rio Tinto gossan ores

Jarosite-type minerals are the major silver carriers in the gossan ores from Rio Tinto (Spain). Two types of minerals were found: one corresponding to beudantite variable enriched in sulfate; the other is potassium jarosite containing various amounts of arsenate and lead. They are isostructural with cell parameters intermediate between those reported for end members. Silver is present in both jarosites as dilute solid solution (230 ppm Ag in average). The cyanidation of potassium jarosite in saturated Ca(OH)₂ at 70–100°C consists of two step in series: a slow step of alkaline decomposition followed by a fast step of Ag complexation from the decomposition solids. The alkaline decomposition is characterized by the simultaneous removal of sulfate and K ions and the formation of an amorphous hydroxy-arsenate of Fe, Pb and Ca. The kinetics are chemically controlled, with an activation energy of 86.5 kJ mol⁻¹. The nature of the alkaline decomposition of beudantite was similar but extremely slow at ≤100°C.     

Kinetics of alkaline decomposition and cyanidation of argentian ammonium jarosite in lime medium

The alkaline decomposition of argentian ammonium jarosite in lime medium is characterized by an induction period and a conversion period in which the sulfate and ammonium ions pass to the solution whereas calcium is incorporated in the residue jointly with iron; this residue is amorphous in nature. The process is chemically controlled and the order of reaction with respect to the hydroxide concentration is 0.4; the activation energy is 70 kJ mol⁻¹. Cyanidation of argentian ammonium jarosite in lime medium presents the same reaction rate in the range of 0–10.2 mol m⁻³ CN⁻; in this range of concentration, the cyanide process can be described, as in other jarosites, in a two-step process: a step of alkaline decomposition that controls the overall process followed by a fast step of silver complexation. For higher cyanide concentration, the order of reaction with respect to cyanide is 0.65, and kinetic models of control by chemical reaction and diffusion control through the products layer both fit well; the activation energy obtained is 29 kJ mol⁻¹; this is indicative of a mixed control of the cyanidation process in the experimental conditions employed. The process is faster than was observed in ammonium jarosite generated in zinc hydrometallurgy (Industrial Minera México, San Luís Potosí, México); it seems that the reaction rate decreases when the substitution level in the jarosite lattice increases; this behavior is similar to that observed for synthetic potassium jarosite and arsenical potassium jarosite from gossan ores (Rio Tinto, Spain) presented in a previous paper.     

Characterization and alkaline decomposition–cyanidation kinetics of industrial ammonium jarosite in NaOH media

A complete characterization was carried out on a jarositic residue from the zinc industry. This residue consists of ammonium jarosite, with some contents of H₃O⁺, Ag⁺, Pb²⁺, Na⁺ and K⁺ in the alkaline “sites” and, Cu²⁺ and Zn²⁺ as a partial substitution of iron. The formula is: [Ag_0.001Na_0.07K_0.02Pb_0.007(NH₄)_0.59(H₃O)_0.31]Fe₃(SO₄)₂(OH)₆. Some contents of franklinite (ZnO^·Fe₂O₃), gunninguite (ZnSO₄·H₂O) and quartz were also detected. The jarosite is interconnected rhombohedral crystals of 1–2 μm, with a size distribution of particles of 2–100 μm, which could be described by the Rosin–Rammler model.The alkaline decomposition curves exhibit an induction period followed by a progressive conversion period; the experimental data are consistent with the spherical particle with shrinking core model for chemical control. The alkaline decomposition of the ammonium jarosite can be shown by the following stoichiometric formula:NH₄Fe₃(SO₄)₂(OH)_6(s)+3OH_(aq)⁻→(NH)_4(aq)⁺+3Fe(OH)_3(s)+2SO_4(aq)²⁻.The decomposition (NaOH) presents an order of reaction of 1.1 with respect to the [OH⁻] and an activation energy of 77 kJ mol⁻¹. In NaOH/CN⁻ media, the process is of 0.8 order with respect to the OH⁻ and 0.15 with respect to the CN⁻. The activation energy was 46 kJ mol⁻¹. Products obtained are amorphous. Franklinite was not affected during the decomposition process. The presence of this phase is indicative that the franklinite acted like a nucleus during the ammonium jarosite precipitation.     

从提锂母液制取氟化钾的研究

将提锂母液与氢氟酸反应，使母液中所有金属元素转化成氟化物。分离出溶解度小的氟化铝、氟化锂、氟化钠等。分离后的溶液进行浓缩，分步析出氟化钠、氟化钾和铷铯氟化物。     

粉末压片制样-X射线荧光光谱法测定锂云母中铷、铯及主量组分

锂云母中铷、铯及主量元素的分析一般采用化学湿法,前处理过程复杂。实验采用粉末压片制样-X射线荧光光谱法(XRF)对锂云母中铷、铯及主量组分(二氧化硅、三氧化二铝、全铁、氧化钙、氧化钾、氧化钠)进行了测定。采用锂矿石标准物质和人工合成校准样品制作校准曲线,各组分的均方根为0.0042~0.49。校准曲线采用经验系数和康普顿散射线内标法校正组分间的吸收-增强效应,方法的检出限为3.1~188μg/g。按照实验方法测定锂矿石标准物质GBW 07152中铷、铯及主量组分,结果的相对标准偏差(RSD,n=10)在0.31%~5.0%之间。实验方法用于测定人工合成校准样品(未参与校准曲线的绘制)中铷、铯及主量组分,测定值与理论值吻合良好;测定2个锂云母实际样品中铷、铯及主量组分,测定结果与电感耦合等离子体原子发射光谱法(ICP-AES)的测定值相符。     

Chemical conversions of osmium (VI) sulfite complexes in ammonia–sulfate solutions

It has been found that osmium (VI) sulfite complexes having composition [OsO₂(SO₃)₂(H₂O)₂]²⁻ in ammonia and sulfuric acid solutions enter into reaction of intrasphere substitution resulting in the formation of new complexes of osmium (VI). The rate of their formation depends on the concentration of constituents in the system and the temperature of solutions. Water-soluble ammonia–sulfite complexes of osmium (VI) (final form is [OsO₂(SO₃)₂(NH₃)₂]²⁻) are formed in ammonia-sulfate solutions. These complexes are converted into sulfate derivatives—water-soluble ([OsO₂(SO₃)(SO₄)(NH₃)₂]²⁻) and insoluble ([OsO₂(SO₄)₂(NH₃)₂]²⁻) in solutions containing (NH₄)₂SO₄ and H₂SO₄.     

Characterization of the iron arsenate–sulphate compounds precipitated at elevated temperatures

To help clarify the nature of the iron arsenate–sulphate compounds produced during the autoclave treatment of refractory gold ores and concentrates, systematic synthesis studies were undertaken; in addition to scorodite and Fe(SO₄)(OH), two other compounds, designated as Phase 3 and Phase 4, were identified. Whereas Fe(SO₄)(OH) is predominantly an orthorhombic compound, Phase 3 can have the same composition but is predominantly the monoclinic polytype, the formation of which is promoted by the solid-solution uptake of As; substitution of As results in a corresponding decrease in the OH required to maintain the charge balance; e.g., Fe[(SO₄)_0.60(AsO₄)_0.40]_∑1.00[(OH)_0.6(H₂O)_0.4]_∑1.00. Phase 4 corresponds to Fe(AsO₄)·¾H₂O. In 0.4 M Fe(SO₄)_1.5 (22.3 g/L Fe), 0.41 M (40 g/L) H₂SO₄, 0.09 M (7 g/L) As(V) solutions, sulphate-containing scorodite was formed at 150–175 °C. Phase 3 precipitated at 175–210 °C, but mixtures of Phase 3 and Fe(SO₄)(OH) formed above 210–220 °C. The Fe content of Phase 3 is about 30 mass %, whereas the AsO₄ and SO₄ contents vary widely and in an inversely proportional manner, reflecting the extensive mutual structural substitution of these anions. At 205 or 215 °C, Fe(SO₄)(OH) was precipitated from 0.4 M Fe(SO₄)_1.5 (22.3 g/L Fe), 0.41 M (40 g/L) H₂SO₄ solutions containing < 0.03 M (2 g/L) As(V). Increasing As(V) concentrations enhance the precipitation of Phase 3, but only Phase 4 was precipitated from solutions containing > 0.33 M (25 g/L) As(V). The composition of Phase 4 is nearly constant and it contains < 1 mass % SO₄. Acid concentrations > 0.2 M H₂SO₄ had little effect on the composition of the precipitates. At 205 °C in 0.41 M (40 g/L) H₂SO₄, 0.09 M (7 g/L) As(V) media, mixtures of scorodite and Phase 4 precipitated from 0.0–0.1 M Fe(SO₄)_1.5 (0.0–5.6 g/L Fe) solutions; for Fe(SO₄)_1.5 concentrations > 0.1 M, only Phase 3 formed. To provide a preliminary indication of the solubility of Phase 3 and Phase 4 in tailings impoundments, the various precipitates were leached at room temperature for 40 h in water. The As concentrations dissolved from Phase 3 were consistently < 0.1 mg/L, which suggests that Phase 3 might be an acceptable medium for arsenic disposal. In contrast, the soluble As concentrations from Phase 4 were 1–3 mg/L.     

萃取法从高盐废液中分离铷铯并制备氯化铯产品

采用t-BAMBP－磺化煤油系配置的有机相对含铷、铯的高盐废液进行除钾试验,然后进行萃取分离试验,分别探索了硫酸铝用量与pH对除钾的影响,萃取过程中料液pH、萃取剂浓度、萃取时间、萃取相比、萃取级数对铷、铯萃取率,以及洗涤过程中洗涤相比、洗涤级数对铷铯洗脱率的影响。研究表明,料液pH=12.5、萃取相比O/A=1、选用1 mol/L萃取剂在室温下萃取5 min,铯萃取率可达99.95%。对高盐废液进行11级萃取(6级萃取、3级洗涤、2级反萃)连续试验,有机相中铯萃取率达99%以上,65%的铷留在水相中,可以较好地将铷与铯分离。最终制备出纯度98.3%的氯化铯产品。     

A partial equilibrium model to characterize the precipitation of ferric ion during the leaching of chalcopyrite with ferric sulfate

A partial equilibrium model has been developed and used to characterize the conditions under which precipitation of ferric ion occurs during the dump leaching of chalcopyrite ores. The precipitates which have been considered include amorphous Fe(OH)₃, α-FeOOH (goethite), and Na⁺, K⁺, Ag⁺, Pb²⁺, and H₃O⁺ jarosites. Solution of the model equations makes possible the determination of the concentrations of the solution species during leaching of the mineral. The concentration product for Fe(OH)₃ (am) and α-FeOOH was calculated for changing solution concentrations and compared with the solubility product constants to determine when precipitation would be expected thermodynamically. The K⁺, Na⁺, Ag⁺, and Pb²⁺ concentrations that would be necessary to satisfy the solubility product constants for the corresponding jarosites were calculated for various initial concentrations and varying amounts of O₂ consumption. Formerly Graduate Assistant, Ames Laboratory USDOE and Department of Chemical Engineering, Iowa State University, Ames, IA 50011     

Electrical conductivity of miscibility gap salt systems based on lithium fluoride with alkali metal bromides

The electrical conductivity κ of miscibility gap ionic melts of lithium fluoride with potassium, rubidium, and cesium bromides is measured. The role of the size and temperature factors in migration is discussed for the systems with a predominant Coulomb interaction of particles in the saturation line.