The coprecipitation of magnesium aluminium hydroxocarbonate powders from aqueous solution: Precipitate compositions and coprecipitation mechanisms

Magnesium aluminium hydroxocarbonate hydrates were coprecipitated from mixed metal nitrate solutions, at total C_M = 0.2 M and Mg/Al₂ = 1 ratio, with four sodium hydrogen carbonate-sodium carbonate solutions (of pH 8.1 to 11.5) at ambient temperature. The course of precipitation was monitored by potentiometric (pH) titration, and the compositions of the primary and final precipitates were determined by chemical analysis, infrared spectrophotometry and X-ray diffraction. Precipitation generally occurred through three stages, primary precipitation (of low CO₃ aluminium hydroxocarbonates) at low pH with evolution of carbon dioxide, their dissolution by complexing to form hydroxocarbonatoaluminate anions and then secondary precipitation of the final coprecipitate at higher pHs. The final product from coprecipitation by sodium hydrogen carbonate solution (pH 8.1) was mainly the magnesium hydroxocarbonatoaluminate ‘MAHC I’; the final products from coprecipitation by sodium hydrogen carbonate-sodium carbonate solutions (pH 9.4 and 10.3) were ‘MAHC I’/‘MAHC II’ mixture and ‘MAHC II’/‘MAHC I’ mixture whereas the final product from coprecipitation by sodium carbonate solution (pH 11.5) was a complex mixture if ‘MAHC II’ with ‘MAHC I’ and ‘MAHC III’;

• ‘MAHC I’ was probably Mg₂[Al₄(OH)₁₀(CO₃)₃] · hH₂O,
• ‘MAHC II’ was probably Mg[Al₂(OH)₄(CO₃)₂] · h H₂O whereas
• ‘MAHC III’ was probably Mg[Al₂(OH)₆CO₃] · h H₂O.

     

The precipitation of basic nickel carbonate powders from aqueous solution. Crystallite numbers,composition and final sizes

The precipitation of basic nickel carbonate hydrates was studied from nickel sulphate solutions (concentrations 0.05 M to 1 M) at 96°C, by addition of sodium carbonate, bicarbonate-carbonate and bicarbonate solutions. Precipitate compositions were determined by chemical analysis, thermogravimetric analysis, differential calorimetry and i.r. spectrophotometry; approximate final crystallite sizes and numbers were estimated from combined sedimentation and porosity measurements on precipitate aggregates. Nucleation, and then crystal growth, started after some ‘critical pH’ pH = 7.05 to 7.67 (at CO₃⁻⁻/Ni⁺⁺ ratio = 0.08–0.12); the solution pH then remained constant (until the CO₃⁻⁻/Ni⁺⁺ ratio = 0.8) and then rose to some final value. Nucleus numbers, and thence final crystallite numbers, decreased with increasing bicarbonate content of the precipitating solution and decreasing pH . Precipitate compositions did not vary significantly with reacting ion concentrations but the Ni(OH)₂/NiCO₃ ratios decreased from 2 to 1.4 with decreasing pH : thermal analysis and i.r. spectrophotometry confirmed that the final precipitates were mixtures of olated nickel carbonates and not nickel carbonate-nickel hydroxide mixtures. Final crystallite sizes of the precipitates from 1 M solutions varied approximately from 0.095 to 0.14 micron, for the above pH range.     

The coprecipitation of calcium aluminium hydroxide (calcium hydroxoaluminate hydrate) powders from aqueous solution with sodium hydroxide: Precipitate compositions and percipitation mechanisms

Calcium aluminium hydroxides were coprecipitated from different mixed metal cation solutions — at total C_M = 0.1 M and Ca/Al₂ ratios from 1 to 4 — with sodium hydroxide solution at ambient temperature. The coprecipitations were monitored by potentiometric (pH) titration and the final coprecipitate compositions were examined by chemical analysis, infra-red spectrophotometry and thermal analysis Generally, microcrystalline aluminium hydroxide was first precipitated at pH about 4; this then redissolved on further addition of sodium hydroxide to form hydroxoaluminate anion and polyanion and calcium aluminium hydroxide coprecipitates were formed continuously at pHs from about 9 to above 12. Their compositions were similar to the calcium hydroxoaluminate hydrates formed by direct precipitation from high pH sodium hydroxoaluminate solutions. At Ca/Al₂ ratio = 1, the main phase was probably Ca₂(H₂O)_h[Al₂(OH)₄]₂ with some Al(OH)₃; At Ca/Al₂ ratio = 2, the main phase was probably Ca₂(H₂O)_h[Al₂(OH)₁₀] dehydrating to Ca₂[Al₂O(OH)₈]; At Ca/Al₂ ratios = 3–4, the main phase was Ca₂(H₂O)_h[Al₂(OH)₁₀] with increasing amounts of Ca₄(H₂O)_h(OH)₄[Al₂(OH)₁₀] and 5–10 percent adsorbed or post-precipitated Ca(OH)₂.     

The precipitation of alkaline-earth metal polymetaphosphate hydrate powders from aqueous solution. Nucleation and crystal growth processes,final precipitate compositions and crystal sizes

The precipitation of barium, strontium, calcium and magnesium polymetaphosphate hydrates was studied from aqueous solutions of initial metal salt concentrations from 0.001 to 3 M at 20 °C; equivalent sodium polymetaphosphate solutions were added to the alkaline-earth metal chloride solutions. Precipitate compositions were determined by chemical analysis, paper chromatography, potentiometric analysis, thermogravimetric and differential thermal analysis and infra-red spectrophotometry; final crystallite morphologies and sizes were studied by scanning electron microscopy and X-ray powder diffraction. Nucleation rates and nucleus numbers (at the end of the induction periods) were very high; crystal numbers varied from 10¹⁴ to 10¹⁵ at the critical concentrations to above 10¹⁷ per 1. solution. Crystal growth rates were also very high and varied as the fourth power of the initial metal salt concentration. High molecular-weight metal polymetaphosphate hydrates were precipitated from the more dilute solutions (0.001 to 0.025 M) while increasing amounts of the more soluble intermediate and low molecular-weight products were precipitated from the more concentrated solutions. Washing with cold water removed the tri- and tetralinear and cyclic phosphate products. The magnesium salts were not precipitated even from 3 M aqueous solutions. The precipitates from aqueous (NaPO₃(I))_n (n = 12) solutions had the compositions (BaP₂O₆ · 2.5 H₂O)₆, (SrP₂O₆ · 3 H₂O)_n and (CaP₂O₆ · 4 H₂O)_n while the magnesium salt precipitate from 20 percent aqueous acetone solution had the composition (MgP₂O₆ · 4 H₂O)_n, the precipitate n values varied from 19 to 13. The precipitates from aqueous (NaPO₃(II))_n (n = 20) solutions contained 0.5n to n additional adsorbed water molecules; these precipitate n values varied in turn from 40 to 26. The final precipitate powders consisted of ‘spherules’ of highly microcrystalline or amorphous polymer glass; the spherule diameters were about 0.2 μm at the critical concentrations and decreased to below 0.05 μm with increasing solution concentrations.     

The Coprecipitation of Zinc Aluminium Hydroxide Powders from Aqueous Solution with Sodium Hydroxide: Precipitate Compositions and Coprecipitation Mechanisms

Zine aluminium hydroxides were coprecipitated from different mixed metal cation solutions, at C_{M tot} = 0.1 M and at Zn/Al₂ ratios from 1 to 4, with sodium hydroxide solution. The coprecipitations were monitored by potentiometrie (pH) titration and the final coprecipitate compositions were examined by chemical analysis, infra-red spectrophotometry and thermal analysis. Generally, microcrystalline aluminium hydroxide was first precipitated at pH about 4; this then partially redissolved on further addition of sodium hydroxide (to form hydroxoaluminate anion) and zinc aluminium hydroxide coprecipitates were formed continuously at pHs from 5.5–6 to above 9. Their compositions were similar to the magnesium hydroxoaluminate coprecipitated from magnesium aluminium solutions. At Zn/Al₂ ratio = 1, the main phase was probably Zn(H₂O)_n [Al(OH)₄]₂; at Zn/Al₂ ratio = 2, the main phase was probably Zn₂(H₂O)_n [Al₂(OH)₁₀], whereas at Zn/Al₂ ratio = 4, the main phase was probably Zn(H₂O)_n(OH)₄[Al₂(OH)₁₀].     

The precipitation of magnesium hydroxoaluminate hydrate powders from sodium hydroxoaluminate solutions: Precipitate phases and precipitation mechanisms

Magnesium hydroxoaluminate hydrates were precipitated from different sodium hydroxoaluminate and hydroxoaluminate-hydroxide solutions at ambient temperature, at C_Al = 0.1 M, OH/Al ratios = 4–9 and XS OH/Al ratios = 1–6. The precipitations were monitored by potentiometric (pH) measurements while the final precipitate compositions were examined by chemical analysis, infra-red spectrophotometry and thermal analysis. At solution OH/Al ratio = 4, the main precipitate phase at 20°C was Mg(H₂O)_n[Al(OH)₄]₂ admixed with some Al(OH)₃; at solution OH/Al ratio = 5, the main phase was Mg₂(H₂O)₄[Al₂(OH)₁₀]; at solution OH/Al ratio = 7, the main phase was Mg₄(H₂O)_n(OH)₄[Al₂(OH)₁₀] while at solution OH/Al ratio = 9, the main phase was Mg₆(H₂O)_n(OH)₈[Al₂(OH)₁₀] admixed with some Mg(OH)₂. These hydrates were dehydrated at 60–100°C probably to the compounds Mg₂[Al₂O₃(OH)₄], Mg₄(OH)₄[Al₂O₃(OH)₄] and Mg₆(OH)₈[Al₂O₃(OH)₄], respectively.     

The precipitation of calcium hydroxoaluminate hydrate powders from sodium hydroxoaluminate solutions: Precipitate phases and precipitation mechanisms

Calcium hydroxoaluminate hydrates were precipitated from different sodium hydroxoaluminate and hydroxoaluminate-excess hydroxide solutions at ambient temperature (at C_Al = 0.1 to 0.3 M and at XS OH/Al = 0 to above 8). The precipitations were monitored by potentiometric (pH) measurements. Precipitate morphologies were examined by optical microscopy and precipitate compositions were determine by chemical analysis, infra-red spectrophotometry and thermal analysis. Generally at OH/Al ratios of 4 to 4.5 (XS OH/Al = 1 to 1.5), the compound 2 CaO · · Al₂O₃ · 8 H₂O (C₂AH₈) was precipitated with some aluminium hydroxide; then at OH/Al ratios of 5 to above 11 (XS OH/Al = 2 to above 8), the compound 2 CaO · Al₂O₃ · 8 H₂O was precipitated with increasing amounts of the compound 4 CaO · Al₂O₃ · 13 H₂O (C₄AH₁₃).     

The precipitation of transition metal oxalate powders from aqueous solution. Crystal numbers and final sizes

The precipitation of manganous, ferrous, cobalt, nickel and copper oxalate hydrates was studied from equivalent solutions of concentrations from 0.001 to 0.3 M at pHs 7 to 6, by optical microscopy and other methods. Crystals growth started after induction periods: the precipitations were heterogeneously nucleated at low supersaturations and homogeneously nucleated at medium to high supersaturations. The crystal numbers of the final precipitates depended on the number of nuclei (and crystallites) formed during the induction periods. At medium to high supersaturations, crystal numbers increased with increasing initial metal oxalate complex ion concentrations according to the relation. N = N₁C_mox^β, where β was 5. The N values increased in the order Mn ≪ Fe < Co < < Ni < Cu. The final crystal lengths, in this range, then decreased with increasing metal oxalate complex ion concentrations according to the relation l_fin = l₁/C_mox^γ, where γ was 1.3. For precipitations from solution of any concentration, smaller crystals were generally obtained in the precipitates of the metal oxalate of lower solubility; nickel oxalate precipitations were the exception to this.     

The precipitation of calcium carbonate powders from aqueous solution with slow development of supersaturation. Induction periods,crystal numbers and final sizes

The precipitation of calcium carbonate was studied by slow addition of anion solution to excess cation solution and by slow mixing of equivalent cation land anion solutions at 20 °C: the final solute concentrations (C_fin were varied from 0.01 to 0.75 mole 1⁻¹ while the rates (R) of addition of ions were varied from 0.06 to 6 · 10⁻³ ion 1⁻¹ sec⁻¹. At first, mainly heterogeneous nuclei formed continuously during induction periods; then, as the metal salt concentration in solution increased, some more heterogeneous nuclei formed but homogeneous nucleation soon predominated. The second nucleation process probably attained its maximum rate when the metal salt concentratio in solution reached its maximum value (C_max) and then probably terminated quite rapidly. Some further nuclei also formed during the growth process when crystal growth was prolonged. The final nucleus numbers (N) (and thence the crystal numbers) for slow precipitations from dilute solutions were then rather higher than the optimum number N∞ (het) of heterogeneous nuclei in the solution; nucleus numbers then increased with increasing maxing rate according to the relations . These numbers were similar to those noted for rapid precipitation – onto homogeneous nuclei – from calcium carbonate solutions of concentrations somewhat lower than the C_max values. The final average crystal lengths of any precipitate then generally varied with mixing rate according to the relations, . where l₁ values increased with (C_fln)^0.33.     

Kinetics of sodium fluosilicate precipitation

The formation of Na₂SiF₆ by discontinuous precipitation of dilute H₂SiF₆ with a 40% excess of an aqueous solution of NaCl under various conditions was studied. The values of induction time, number of crystals formed, their final size and their habit were determined during precipitation from solutions, whose initial supersaturation was 2 < S < 11. At S < 7–8 the crystals were formed by heterogeneous nucleation, whereas at S ≳ 7–8 homogeneous nucleation mechanism began to prevail. Once formed, the Na₂SiF₆ crystals were growing according to the screw-dislocation mechanism till they reached visible size; the corresponding values of kinetic order of nucleation and of the growth rate constant were g = 1.35 and k_g = 4.32 × 10⁻⁸ cm^2.05 sec⁻¹ g^−0.35, resp. The value of interfacial tension on the phase boundary Na₂SiF₆ crystal — saturated solution was determined (σ ∼ 52 erg/cm²). The resulting Na₂SiF₆ crystals conformed to log-normal distribution irrespective of conditions of precipitation. The dependence of the final size of crystals on supersaturation exhibited a maximum at S ∼ 6. Crystals of Na₂SiF₆ had a hexagonal habit, which was near to a spherical form at lower supersaturations, while dendritic crystals were formed at higher supersaturations.     

The coprecipitation of magnesium hydroxide aluminium hydroxide powders from aqueous solution with sodium hydroxide: Precipitate compositions and coprecipitation mechanisms

Magnesium aluminium hydroxides were coprecipitated from different mixed metal cation solutions — at total C_M = 0.1 M and Mg/Al₂ ratios from 1 to 6 — with sodium hydroxide solution at ambient temperature, with different pre-ageing conditions for the aluminium hydroxide pre-precipitate. The coprecipitations were monitored by potentiometric (pH) titration and the final precipitate compositions were examined by chemical analysis, infrared spectrophotometry and thermal analysis. Magnesium hydroxide was coprecipitated onto completely recrystallised aluminium hydroxide as a simple mixture. Generally, with no to three days pre-ageing, microcrystalline aluminium hydroxide was first precipitated at pH about 4; this then partially redissolved on further addition of sodium hydroxide (to form hydroxoaluminate anion) and magnesium aluminium hydroxide coprecipitates were formed continuously at pHs from 8.0–8.7 to 12.0–12.5. Their compositions were similar to the magnesium hydroxoaluminate hydrates formed by direct precipitation from high pH sodium hydroxoaluminate solutions.      

The Precipitation of Alkaline-Earth Metal Polyacrylate Hydrate Powders from Aqueous Solution: Ionic Equilibria,Precipitate Compositions and Morphologies

The precipitation of barium, strontium, calcium and magnexium polyacryate hydrates was studied from equivalent aqueous solutions of initial concentrations 0.03 M to 0.30 M at ambient temperature: sodium polyacrylate (m. wt = 30,000 to 300,000) was added to metal chloride solution. The final yields of precipitate increased with decreasing solubility and/or peptisation (Ba > Sr > Ca > Mg) and increasing molecular weight of the polyacrylate; the precipitates had the compositions [BaA(COO)₂ · 1–2H₂O]_n, [SrA(COO)₂ · 1–2 H₂O]_n, [CaA(COO)₂ · 2 H₂O]_n and [MgA(COO)₂ · 2 H₂O]_n. The final yields of the precipitates from sodium polyacrylate solutions were far lower and these had the compositions [Na_2αM_1-αCA(COO)₂ · 2 H₂O]_n; A =  CH CH₂ CH . The metal polyacrylate hydrate powders consisted of microcrystalline ‘spherules’; their average diameters were from 0.03–0.05 μm (for lower m. wt products) to 0.01 to 0.02 μ,m (for higher m. wt products).     

The Coprecipitation of Magnesium Iron (III) Hydroxide Powders from Aqueous Solution: Precipitate Compositions and Coprecipitation and Ageing Mechanisms

Series of magnesium iron(111) hydroxides were coprecipitated at ambient temperature from different mixed metal cation solutions, at C_{M tot} = 0.1 M and Mg/Fe₂ ratios from 4 to 1/4, with sodium hydroxide solution. The relevant single precipitations and the coprecipitations were monitored by potentiometric (pH) titration and the final coprecipitate compositions were examined by chemical analysis, infra-red spectrophotometry and thermal analysis. The coprecipitates onto aged α-FeOOH were simple mixtures of α-FeOOH and Mg(OH)₂. The main coprecipitates were either «molecular inclusion mixtures» of microcrystalline α-FeOOH with excess Mg(OH)₂ or similar mixtures of Mg(OH)₂ with excess α-FeOOH and some ten-twenty percent (relative to the Mg content) of magnesium hydroxo-ferrate(III) hydrate Mg[Fe(OH)₄]₂ · h H₂O. The coprecipitates aged in alkaline magnesium hydroxide suspension at 20 °C and 40 °C were mixtures of Mg(OH)₂, α-FeOOH and forty to ninety percent (relative to the Mg content) of Mg[Fe(OH)₄]₂ · h H₂O. The related α-FeOOH NaOH and α-FeOOH Mg(OH)₂ equilibria and the different coprecipitation mechanisms are discussed.     

The coprecipitation of magnesium hydroxoaluminate hydrates from aqueous solution with ammonium hydroxide: Precipitate compositions and coprecipitation mechanisms

Magnesium hydroxoaluminate hydrates were coprecipitated from different mixed metal cation solutions at Mg/Al₂ ratios from 1 to 4 by ammonium hydroxide. The coprecipitations were monitored by potentiometric titration and the final precipitate compositions were examined by chemical analysis, X-ray diffraction, infra-red spectrophotometry and thermal analysis. The process of coprecipitation was similar to that for coprecipitation with sodium hydroxide but large excess of ammonium hydroxide was required for complete reaction at pHs from about 8 to 10.

• At Mg/Al₂ = 1, the main phase was probably Mg(H₂O)_h [Al(OH)₄]₂;
• at Mg/Al₂ = 2, the main phase was probably Mg₂(H₂O)_h [Al₂(OH)₁₀];
• at Mg/Al₂ = 4, the main phase was probably (MgOH₄) (H₂O)^h [Al₂(OH)₁₀].

     

The Precipitation of Alkaline-Earth Metal Carbonate Powders from Aqueous Solution. Crystal Numbers and Final Sizes

The precipitations of magnesium carbonate trihydrate, basic magnesium carbonate and calcium, strontium and barium carbonates was studied from equivalent solutions of concentrations from 0.0005 M to 1M, at pHs from 10 to 7, by optical microscopy and other methods. Crystal growth started after induction periods: the precipitations of the more sparingly-soluble metal carbonates — mainly studied at medium to high supersaturation — were homogeneously nucleated while the magnesium carbonate trihydrate precipitations — studied at low supersaturations at pH ≦ 7.6 — were heterogeneously nucleated. The crystal forms and numbers of the final precipitates depended on the type and numbers of nuclei (and crystallites) formed during the induction periods. Crystal numbers generally increased with increasing initial mean metal carbonate concentration according to the relation N = N₁C_MCO3^β; β was 3 for the metal carbonate precipitations and β was 4 for the basic magnesium carbonate precipitations. N₁ values increased in the order basic MgCO₃ (at pH ≧ 9), or MgCO₃ · 3H₂O (at pH ≦ 7.6) < CaCO₃ < SrCO₃ < BaCO₃. The final crystal lengths then generally decreased, from maximum values, with increasing initial concentration according to the relation l_fin = l₁/C^γ, where γ was 0.7 and 1.0. For precipitation at any concentration and pH, smaller crystal sizes were generally obtained in precipitates from solutions of the metal carbonate of lower solubility.     

Spontaneous precipitation of calcium silicate hydrate in aqueous solutions

Calcium silicate hydrates (C‐S‐H) are very important not only for their contribution to the development of cement and concrete properties but also for use as fillers and in silicate glasses. In the present work, the thermodynamics and the kinetics of the spontaneous precipitation of C‐S‐H from aqueous solutions were investigated over the pH range 10‐12 at 25 °C. The thermodynamic driving force was calculated taking into consideration all equilibria involved in the supersaturated solutions. In the range of the solution supersaturation values examined the precipitation occurred spontaneously, with the exception of the series of experiments done at pH 12.0, where induction times preceded the appearance of the precipitate. The rates were measured at constant pH as a function of the solution supersaturation and were found to depend strongly on the solution supersaturation, pH and on the total calcium to total silicate molar ratio in solution. Fit of the kinetics results in a power law relating rates of precipitation with respect to C‐S‐H precipitated, suggested a surface diffusion controlled mechanism for the formation of C‐S‐H. The precipitated solids did not show significant morphological differences at different pH values. From the induction times preceding the spontaneous precipitation at pH 12.0, a value of 30 mJm^‐2 was calculated for the surface energy of C‐S‐H. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The morphology of witherite and strontianite grown in Silica Gel,by slow precipitation and on hydrothermal conditions

Both the gel method, slow precipitation, hydrogen carbonate transport at room temperature as well as hydrothermal transport in a carbon dioxide solution and the hydrothermal decomposition of the oxalates were used to grow BaCO₃ and SrCO₃. The morphology of the resulting crystals is described and compared with respect to theoretical considerations including the Donnay-Harker rule and the PBC theory.     

The precipitation of barium hydroxoaluminate hydrate powders from sodium hydroxoaluminate solutions: Precipitate phases and precipitation mechanisms

Barium hydroxoaluminate hydrates were precipitated from different sodium hydroxoaluminate solutions at 20 °C; C_Al varied from 0.1 to 0.5 M and initial Ba/Al₂ ratios ( = excess OH/Al ratios) varied from 1 to 7. Precipitate compositions were determined by chemical analysis, infra-red spectrophotometry and thermal analysis. The compound BaO · Al₂O₃ · 7 H₂O was precipitated at initial Ba/Al₂ ratios of one to well above two while the compound 2 BaO · Al₂O₃ · 5 H₂O was only precipitated over a narrow range of concentrations. The compound Ba(OH)₂ · 8 H₂O was precipitated from solutions of high hydroxide and barium ion concentrations. The ionic equilibria and precipitation mechanisms in different solutions are discussed.     

Ortho-metalation and carboxylate coordination in the reaction between the dipotassium salt of phthalic acid and Cp*Ir(PMe3)Cl2: X-ray diffraction structure of Cp*Ir(PMe3)[C6H3(CO2)(CO2H)]

The cyclopentadienyl complex Cp*Ir(PMe₃)Cl₂ reacts with the dipotassium salt of phthalic acid in the presence of AgPF₆ via chloride substitution to give the ortho-metalated compound Cp*Ir(PMe₃)[C₆H₃(CO₂)(CO₂H)]. This new compound has been isolated by recrystallization and has been characterized in solution by ¹H and ¹³C NMR spectroscopies, and the solid-state structure has been verified by X-ray crystallography. Cp*Ir(PMe₃)[C₆H₃(CO₂)(CO₂H)] crystallizes in the monoclinic space group P2₁/c, a = 9.1010(6) Å, b = 16.715(1) Å, c = 14.3965(9) Å, = 108.24(1)°, V = 2080.0(2) ų, Z = 4, and d _calc = 1.813 mg/m³; R = 0.0276, R _w = 0.0810 for 2730 reflections with I > 2(I). Coordination of the benzene ring to the iridium center via one of the carboxylate groups and ortho-metalation of the C–H moiety that was to the iridium-bound carboxylate group is confirmed.     

The precipitation of sparingly-soluble acid,neutral and basic metal salts from aqueous solution: Ionic equilibria at different pHs,precipitate phases and precipitation mechanisms

The precipitations of the sparingly-soluble acid, neutral and basic salts of the divalent cations beryllium, magnesium, calcium, strontium, barium, manganese (II), iron (II), cobalt (II), nickel (II), copper (II), zinc, cadmium, mercury (II), tin (II) and lead (II) with the inorganic anions sulphate, chromate, molybdate, monohydrogen phosphate, phosphate, and carbonate (from supersaturated aqueous solutions) are surveyed. The different types of ionic equilibria (cation hydrolysis, anion hydrolysis, ion-pair formation) that may influence these precipitations, at different pHs and ionic concentrations, are examined. The crystalline phases precipitated at different pHs are tabulated and the precipitation mechanisms (at different pHs) are analysed.