The detection of potassium sulfate in excess of potassium pyrosulfate

X-Ray diffraction, infrared, and raman spectroscopic methods were investigated for the detection of K₂SO₄ in excess of K₂S₂O₇ in solid solutions.The X-ray diffraction lines of K₂SO₄ were found to be overlapped by the diffraction pattern of K₂S₂O₇ and infrared studies indicated that K₂SO₄ absorption bands corresponded to regions of strong absorption in K₂S₂O₇. The detection of sulfate could not be carried out by the X-ray diffraction and infrared methods. However, the raman method indicated that a strong and narrow K₂SO₄ band at 981 cm^?1 could unambiguously be used for the detection of sulfate in solid solutions of K₂SO₄ in K₂S₂O₇, as pyrosulfate showed no absorption around this band.     

Thermal and X-Ray studies of reactions between scandium(III) oxide and sodium or potassium persulfates

TG, DTG, and DTA experiments were carried out to elucidate the influence of Sc₂O₃ on the thermal decomposition of Na₂S₂O₈ and K₂S₂O₈ under a static (air) atmosphere from ambient to 1050°C, using a derivatograph. X-Ray diffractometry has been employed to identify the intermediate and final decomposition products. Different Sc₂O₃ Na₂(K₂)S₂O₈ molar ratios were investigated and the 1 : 3 ratio found to be the one that gives stoichiometric reactions with either of these salts. Sc₂O₃ was found to react at 250 and 440°C with the thermally produced Na₂S₂O₇ yielding Sc₂(SO₄)₃. The scandium(III) sulfate was thermally stable up to 840°C. Similarly, the oxide reacts stoichiometrically at 420°C to produce KSc(SO₄)₂, a double salt which began to decompose at 840°. Moreover, three new crystalline phase-transformations were detected for Sc₂(SO₄)₃ at 640, 695, and 735°C.     

High temperature reactions of titanium(IV) oxide with some alkali persulfates and their decomposition products

The solid state reactions between TiO₂ and Na₂S₂O₈ or K₂S₂O₈ have been investigated using TG, DTG, DTA, IR, and X-ray diffraction studies in the range of 20 to 1000°C.It has been shown that TiO₂ reacts stoichiometrically (1 : 1) with Na₂S₂O₈ in the range of 160 and 220°C forming the complex sodium monoperoxodisulfato—titanium(IV) as characterized by IR and X-ray analysis. The new complex then decomposes into the reactants above 190°C.An exothermic reaction has been observed between TiO₂ and molten K₂S₂O₇ at mole ratio 1:2 respectively and higher, in the range of 280 and 350°C. The IR and X-ray analyses have shown the formation of a complex namely, potassium tetrasulfato titanium(IV) for which the formula and structure have been proposed. This complex decomposes at higher temperatures into K₂SO₄ and a mixed sulfate of potassium and titanium. The mixed sulfate melts at 620°C and decomposes into K₂SO₄, TiO₂, and the gaseous SO₃.On the other hand, Na₂S₂O₈ decomposes in a special mode producing a polymeric product of Na₁₀S₉O₃₂. Decomposition of this species occurs after melting at 560°C into Na₂SO₄ and sulfur oxides. The decomposition reaction has been proved to be catalysed by TiO₂ itself.     

Cyclic Voltammetric Behavior of Uranyl ion in Sulfuric Acid Solutions. Application to Some Nuclear Materials Characterization

Abstract

The U(VI) reduction at mercury electrode in sulfuric acid solutions was examined by cyclic voltammetry (C. V.). A diffusion coefficient, D, was (5.30 ± 0.08) × 10^?6 cm²/sec was obtained for the depolarizer at 25.0±0.2°C in 1 N K₂SO₄ (pH = 2). In 1 N K₂SO₄/1 N H₂,SO₄ systems the disproportionation of U(V) was found to occur with the constant rate of K_d/[H⁺] = 6.500 ± 1.000 M^?2 sec^?1.

In 1 M H₂SO₄ supporting electrolyte pure kinetic control was achieved over the range of scan rates and uranyl concentration (C) investigated, hence linear correlation between cathodic peak current and C (above 5x10^?6 M) was obtained. Strong complexing oxyanions, such as phosphate and pyrosulphate, do not interfere with the cathodic peak current. Rapid determination of O/U ratios in uranium oxides and of U in mixed U-Th materials were performed respectively in 1 M H₂SO₄/1.5 M H₃PO₄ and 1 M H₂SO₄/0.2 M K₂S₂0₄ supporting media, with a reproducibility of ± 1.3% standard deviation.     

Molten potassium pyrosulfate: The reactions of seven metal oxalates

The reactions of Li₂C₂O₄, Na₂C₂O₄, K₂C₂·H₂O, CaC₂·H₂O, ZnC₂O₄, La₂(C₂O₄)₃ and K₂TiO(C₂O₄)₂· 2H₂O with K₂S₂O₇ were investigated using thermal methods of analysis. Reaction products were analysed by various techniques. It was found that anhydrous oxalates reacted with K₂S₂O₇, evolving a mixture of CO₂ and CO with the formation of K₂SO₄ and the corresponding metal sulfates, which, in the reactions of ZnC₂O₄ and K₂TiO(C₂O₄)₂ 2H₂O, probably existed as K₂[Zn(SO₄)₂] and K₄[Ti(SO₄)₄], respectively. Water was found to be an additional product in the hydrated metal oxalate reactions. The stoichiometries of these reactions have been established from the thermogravimetric and acidimetric results.     

Phase ratios in the K2O-V2O4-SO3 system at high sulfur trioxide concentrations

Phase ratios in the three-component oxide system K₂O-V₂O₄-SO₃ in the region of the sulfur trioxide concentrations corresponding to its concentrations in the active component of vanadium catalysts for SO₂ to SO₃ conversion have been studied using powder X-ray diffraction, IR spectroscopy, microscopy, and chemical analysis. Four individual compounds (K₂VO(SO₄)₂, K₂(VO)₂(SO₄)₃, K₂VO(SO₄)₂S₂O₇, and K₂(VO)₂(SO₄)₂S₂O₇) and K₂(VO)₂(SO₄)₂S₂O₇ and VOSO₄-base solid solutions of composition K₂(VO)_2+x (SO₄)_2+x S₂O₇ (0 ≤ x ≤ 1.5) were found in the system. K₂VO(SO₄)S₂O₇ and K₂(VO)₂(SO₄)₂S₂O₇ lose their sulfur trioxide when heated above 350°C under an inert atmosphere, and convert to K₂VO(SO₄)₂ and K₂(VO)₂(SO₄)₃, respectively. This implies that K₂VO(SO₄)₂S₂O₇ and K₂(VO)₂(SO₄)₂S₂O₇, as well as K₂(VO)_2+x (SO₄)_2+x S₂O₇ solid solution, cannot exist in the active component of real industrial catalysts.     

Zum System V2O5?K2SO4

The phase diagram of the system V₂O₅? K₂SO₄ was established by means of X-ray diffraction and DTA. An endothermal reaction leads to the compound 5V₂O₅·3K₂SO₄ which melts at 510°C, crystallizes needle-shaped and forms hydrates. Eutectics occur at 31 (505°) and 55 mole-% K₂SO₄ (455°C).     

Raman spectroscopy evidence of 1:1:1 complex formation during dissolution of WO3 in a melt of K2S2O7:K2SO4

Highly inert yellow solid WO₃ was found to be soluble in considerable amounts in molten K₂S₂O₇ at elevated temperatures (∼650 °C), if only similar molar amounts of sulfates were also present. The dissolution reaction of WO₃ into a melt consisting of a 1:1 molar mixture of K₂S₂O₇ and K₂SO₄ was studied in detail, and Raman spectroscopy was used to characterize the products. In combination with single crystal X-ray crystal structure determination, it was shown that a new dimeric compound, K₈[{W^VIO₂(SO₄)₂}₂(μ-SO₄)₂], was formed and its assigned Raman spectrum at room temperature is given. The WO₂²⁺ cores of the dimeric complex have their symmetrical and antisymmetrical stretching modes ν₁(WO₂²⁺) and ν₃(WO₂²⁺) at around 1054 (strong) and 1042 (weak), and the bending mode ν₂(WO₂²⁺) at around 292 (medium intensity), respectively (positions given in cm⁻¹).     

K<Subscript>3</Subscript>VO<Subscript>2</Subscript>(SO<Subscript>4</Subscript>)<Subscript>2</Subscript>: Formation conditions,crystal structure,and physicochemical properties

Potassium oxosulfatovanadate(V) K₃VO₂(SO₄)₂ has been obtained by solid-phase synthesis from K₂SO₄, K₂S₂O₇, and V₂O₅ (2: 1: 1), and its formation conditions, crystal structure, and physiochemical properties have been studied. The conversions of K₃VO₂(SO₄)₂ in contact with potassium vanadates and other potassium oxosulfatovanadates(V) are considered in terms of phase relations in the K₂O-V₂O₅-SO₃ system, which models the active component of vanadium catalysts for sulfur dioxide oxidation into sulfur trioxide. The X-ray diffraction pattern of K₃VO₂(SO₄)₂ is indexed in the monoclinic system (space group P2₁) with unit cell parameters of a = 10.0408(1) Å, b = 7.2312(1) Å, c = 7.3821(1) Å, β = 104.457(1)°, Z = 2, and V = 519.02 ų. The crystal structure of K₃VO₂(SO₄)₂ is built from [VO₂(SO₄)₂]^3? complex anions, in which the vanadium atom is in an octahedral oxygen environment formed by two terminal oxygen atoms (V-O(6) = 1.605(7) Å, V-O(10) = 1.619(7) Å and four oxygen atoms of the two chelating sulfate anions. The vibrational spectra of K₃VO₂(SO₄)₂ are analyzed using these structural data.     

Synthesis and thermal decomposition of potassium peroxotitanate to K2Ti2O5

Potassium peroxotitanate was synthesized by the peroxo method. During the thermal decomposition K₂Ti₂O₅ can be obtained. The isothermal conditions for decomposition of K₂[Ti₂(O₂)₂(OH)₆]·3H₂O were determined on the base of DTA, TG and DSC results. DTA and TG curves were recorded in the temperature range 20 and 900°C at a heating rate of 10°C min^–1. The obtained intermediate compounds were characterized by means of quantitative analysis and IR spectroscopy. The mechanism of thermal decomposition of K₂[Ti₂(O₂)₂(OH)₆]·3H₂O to K₂Ti₂O₅ was studied. The optimal conditions for obtaining K₂Ti₂O₅ were determined (770°C for 10 h).     

Equilibria in the system containing chloride and sulphates of potassium and magnesium

Reciprocal salt-pair system 2KC1 + MgSO₄ ⇌ K₂SO₄ + MgCl₂ has been studied at 35° C to eliminate the discrepancies reported by different workers and for correlating the experimental data with natural evaporation of brine (without NaCl) so as to recover potash salts.     

Reaction with SO3 in Ionic Liquids: The Example of K2(S2O7)­(H2SO4)

The ionic liquid 1‐butyl‐3‐methylimidazolium hydrogensulfate, [bmim]HSO₄, turned out to be resistant even to strong oxidizers like SO₃. Thus, it should be a suitable solvent for the preparation of polysulfates at low temperatures. As a proof of principle we here present the synthesis and crystal structure of K₂(S₂O₇)(H₂SO₄), which has been obtained from the reaction of K₂SO₄ and SO₃ in [bmim]HSO₄. In the crystal structure of K₂(S₂O₇)(H₂SO₄) (orthorhombic, Pbca, Z = 8, a = 810.64(2) pm, b = 1047.90(2) pm, c = 2328.86(6) pm, V = 1978.30(8) ų) two crystallographically unique potassium cations are coordinated by a different number of monodentate and bidentate‐chelating disulfate anions as well as by sulfuric acid molecules. The crystal structure consists of alternating layers of [K₂(S₂O₇)] slabs and H₂SO₄ molecules. Hydrogen bonds between hydrogen atoms of sulfuric acid molecules and oxygen atoms of the neighboring disulfate anions are observed.     

A DSC study of benzoic acid: a suggested calibrant compound

It has been found that cobalt(II, III) oxide, Co₃O₄, lowers the thermal decomposition temperature of Na₂S₂O₈ and K₂S₂O₈ by about 25°C by catalysis, and it therefore acts as a P-type semiconductor at high temperature and atmospheric (air) pressure. Also, this oxide reacts at high temperature with sodium or potassium pyrosulfates to form thermally stable sodium cobalt disulfate, Na₂Co(SO₄)₂ and potassium cobalt trisulfate, K₂Co₂(SO₄)₃, respectively. Binary systems, consisting of a 1 : 3 mole ratio (oxide : persulfate), are established as representing the solid state stoichiometric reaction. X-Ray diffractometry is employed to identify intermediate and final reaction products in general. All calculations are based on data obtained from TG, DTG and DTA curves.     

The Decomposition of Aqueous Dithionite and its reactions with polythionates SnO2−6 (n = 3–5) studied by ion-pair chromatography

Aqueous dithionite decomposes at 20°C and pH values not far from 7.0 to give thiosulfate and sulfite from which trithionate may form. Addition of thiosulfate accelerates this reaction only at pH < 6. The pH dependence is explained by formation of HS₂O₃^? ions which are reduced by dithionite to HS^? and SO^2?₃. Sulfide destroys dithionite by nucleophilic cleavage, probably with formation of sulfoxylate and thiosulfite ions. The polythionates S_nO^2?₆ (n = 3–5) are reduced by dithionite at pH = 7.0 and 20°C according to S_nO^2?₆ + S₂O^2?₄ + 2 H₂O→S₂O₃^2? + S_n–3SO₃^2? + 4H¹ + 2SO₃^2? The reaction rate rapidly increases with the number n of sulfur atoms. In secondary reactions sulfite attacks S_nO₆^2? ions with thiosulfate formation.     

Phase equilibria in the oxide system Nd2O3–K2O–P2O5

A phase equilibria diagram of the partial system NdPO₄–K₃PO₄–KPO₃ has been developed as part of the research aimed at determining the phase equilibrium relationships in the oxide system Nd₂O₃–K₂O–P₂O₅. The investigations were conducted using thermoanalytical techniques, X-ray powder diffraction analysis and reflected-light microscopy. Three isopleths existing between: K₃Nd(PO₄)₂–K₄P₂O₇, NdPO₄–K₅P₃O₁₀ and NdPO₄–K₄P₂O₇ have been identified in the partial NdPO₄–K₃PO₄–KPO₃ system. Previously unknown potassium-neodymium phosphate “K₄Nd₂P₄O₁₅” has been discovered in the latter isopleth section. This phosphate exists in the solid phase up to a temperature of 890 °C at which it decomposes into the parent phosphates NdPO₄ and K₄P₂O₇. Four invariant points: two quasi-ternary eutectics, E₁ (1057 °C) and E₂ (580 °C) and two quasi-ternary peritectics, P₁ (1078 °C) and P₂ (610 °C), occur in the NdPO₄–K₃PO₄–KPO₃ region.     

Thermodynamics and kinetics of steam splitting over a potassium aluminosilicate electrolyte

A novel system using a potassium aluminosilicate electrolyte under applied potential that is able to split H₂O (or OHˉ) into H₂ and 1/2O₂ (or O₂ ^2-) with higher yields than the value deduced from Faraday"s law is presented. There were three steps by which H₂ and O₂ were generated stoichiometrically, and it was predicted that the high yields were due to the occurrence of chemically endothermic reactions: dehydration of the catalytic cell at a temperature below 100°C (step I), disproportionation of KOH (2KOH→H₂+K₂O₂) at a temperature around 200°C (step II), and disproportionation of K₂O (2K₂O→K₂+K₂O₂) at a temperature above 500°C (step III). So-called Nemca might be caused in the course of step III, since the rate of H₂ was ca 10² times larger than the value deduced from Faraday"s law. This revised version was published online in August 2006 with corrections to the Cover Date.     

From Infinite Chains according to 1∞[Zr(S2O7)4/2] in Zr(S2O7)2 to the unprecedented [Zr(S2O7)4]4– Anion in Ag4[Zr(S2O7)4]

The reaction of ZrCl₄ with oleum (65 % SO₃) in the presence of Ag₂SO₄ at 250 °C yielded colorless single crystals of Zr(S₂O₇)₂ [orthorhombic, Pccn, Z = 4, a = 709.08(6) pm, b = 1442.2(2) pm, c = 942.23(9) pm, V = 963.5(2) × 10⁶ pm³]. Zr(S₂O₇)₂ shows Zr⁴⁺ ions in an eightfold distorted square antiprismatic coordination of oxygen atoms belonging to four chelating disulfate units. Each S₂O₇^2– ion is connected to a further Zr⁴⁺ ion leading to chains according to ¹_∞[Zr(S₂O₇)_4/2]. The same reaction at a temperature of 150 °C resulted in the formation of Ag₄[Zr(S₂O₇)₄] [monoclinic, C2/c, Z = 4, a = 1829.35(9) pm, b = 704.37(3) pm, c = 1999.1(1) pm, β = 117.844(2)°, V = 2277.6(2) × 10⁶ pm³]. Ag₄[Zr(S₂O₇)₄] exhibits the unprecedented [Zr(S₂O₇)₄]^4– anion, in which the central Zr⁴⁺ cation is coordinated by four chelating disulfate units. Thus, in Ag₄[Zr(S₂O₇)₄] the ¹_∞[[Zr(S₂O₇)_4/2] chains observed in Zr(S₂O₇)₂ are formally cut into pieces by the implementation of Ag⁺ ions.     

Nd(S2O7)(HSO4): Das erste Disulfat eines Selten‐Erd‐Elementes

Nd(S₂O₇)(HSO₄): The First Disulfate of a Rare Earth Element Light violett single crystals of Nd(S₂O₇)(HSO₄) have been obtained by the reaction of Nd₂O₃ and oleum (30% SO₃) at 200 °C in sealed glass ampoules. The crystal structure (monoclinic, P2₁/n, Z = 4, a = 857.8(1), b = 1061.0(2), c = 972.4(1) pm, β = 99.33(2)°) contains Nd³⁺ in eightfold coordination of oxygen atoms which belong to three HSO₄^– ions and four S₂O₇^2– groups. One of the latter acts as bidentate ligand. Hydrogen bonding is observed between the H atom of the HSO₄^– ion and the non‐coordinating O atom of the S₂O₇^2– group.     

Solubility study of sodium, potassium and calcium sulfates and chlorides, in ammonia

Solubility of sodium, potassium and calcium sulfates and chlorides in 28% ammonia solution was determined through monitoring conductivity measurements and kinetics of solids dissolution as a function of temperature and stirring time. The major findings of the present study show that Na₂SO₄ and K₂SO₄ solutions conductivity follow straight linear segments with different slopes. However, in case of NaCl, KC1, CaCl₂ and CaSO₄ · 2H₂O, conductivity curves were continuous, monotonous and reach constants maximum values. The hypothesis of complex formation or dissolution via intermediaries such as NaNH₄SO₄ and KNH₄SO₄ salts seams to be true, through X-ray diffraction study of resulting deposits. Furthermore, the dissolution rates at 25°C of potassium and calcium chlorides in ammonia solution are higher than that reported in the literature for water. In fact, ammonia significantly reduces the solubility of K₂SO₄; conversely, a slight increase in this parameter was observed for CaSO₄.     

Aqueous polymerization of methacrylamide with potassium persulphate/thiomalic acid redox pair

Summary Methacrylamide was polymerized in aqueous medium at 35 ± 0.2 °C with the redox pair K₂S₂O₈/ thiomalic acid (mercaptosuccinic acid) in dark under nitrogen atmosphere. The effect of monomer, K₂S₂O₈ and thiomalic acid concentrations and temperature on the rate of polymerization was studied. The kinetics of polymerization was followed iodometrically.The role of the addition of complexing metal ions and a series of aliphatic alcohols was also investigated. The initial rate of polymerization was found to be independent of the concentration of thiomalic acid. Rate may be expressed by the following equation:R _p [M]^1.5[K₂S₂O₈]^0.76. The energy of activation was found to be 9.0 Kcal/deg/mole.With 4 figures