Precipitation of some slightly soluble salts using emulsion liquid membranes

Emulsion liquid membranes were used for precipitation of different sparingly soluble salts: calcium oxalate, copper oxalate, nickel oxalate, cobalt oxalate, lanthanum oxalate, calcium phosphate, cobalt phosphate, copper phosphate, lanthanum phosphate, barium sulphate, strontium sulphate and calcium sulphate. For the transport of a desired cation or anion from the feed into the stripping solution, where the precipitation occurred, one of the commercial ligands (bis(2-ethylhexyl)phosphoric acid, D2EHPA; 2-hydroxy-5-nonyl-acetophenone oxime, LIX 84; trioctylamine, ALAMIN 336) dissolved in kerosene, was used as a carrier. The precipitates obtained were characterized by means of transmission electron microscopy, X-ray diffractometry, FT-IR spectroscopy and thermogravimetry. The effect of the transport mechanism on the properties of salt precipitated was studied on calcium and copper oxalate model systems. It was found that copper oxalate hemihydrate and calcium oxalate monohydrate precipitated regardless of whether oxalic acid or a cation (calcium or copper) was transported into the stripping solution. It was also found that the particles of the precipitate were smaller when oxalic acid was transported

Factors influencing the formation of calcium oxalate hydrates in vitro

Općenito uzevši, na proces taloženja iz prezasićenih otopina utječu fizikalno-kemijska svojstva tih otopina, hidrodinamički čimbenici piocesi miješanja reaktanata i taložnoga sustava, kao i prisutnost topljivih nečistoća u sustavu. Zbog važnosti procesa taloženja u brojnim područjima znanosti i tehnike, od izuzetnoga su značaja temeljna istraživanja tih procesa kao i međudjelovanja koja dovode do stvaranja taloga. Obzirom na činjenicu da su kalcijevi oksalati glavni sastojci mokraćnih kamenaca, njihovo izučavanje, kao i izučavanje fizikalno-kemijskih čimbenika koji dovode do njihovoga nastajanja jesu od posebnog značaja u području patološke mineralizacije. Kalcijevi oksalati tvore tri hidratna oblika od kojih je monohidrat (COM) termodinamički stabilan, dok su dihidrat (COD) i trihidrat (COT) metastabilni. Rezultate istraživanja utjecaja brojnih termodinamičkih i kinetičkih čimbenika, kao i potencijalnih inhibitora na nastajanje i transformaciju kalcijevih oksalata pri različitim eksperimentalnim uvjetima, prikazane u ovom pregledu, sadašnji su autori ostvarili i objavili tijekom 1980-ih.Precipitation from supersaturated solutions is in general affected by the physical chemical properties ot the solution, by the hydrodynamics of the system, i.e., by the processes of mixing reactants and stirring the system, as well as by soluble impurities present in the system. Therefore, such a knowledge should be considered in a number of areas where precipitation plays an important role. Since calcium oxalates have been found to be a major crystal constituent of urinary stones, their investigations, as well as investigations of physical chemical conditions relevant for their formation are of particular importance for fundamental research in the field of patological mineralization. Calcium oxalate forms three hydrates. These three hydrates are the thermodynamically stable monohydrate (COM) and the metastable modifications, dihydrate (COD) and trihydrate (COT). The results on investigations of the influence of a number of thermodynamic and kinetic factors, as well as the potential inhibitors, on the hydrate formation and transformation under different experimental conditions had been obtained and published by the present authors during 1980th

Factors influencing the formation of calcium oxalate hydrates in vitro

Općenito uzevši, na proces taloženja iz prezasićenih otopina utječu fizikalno-kemijska svojstva tih otopina, hidrodinamički čimbenici piocesi miješanja reaktanata i taložnoga sustava, kao i prisutnost topljivih nečistoća u sustavu. Zbog važnosti procesa taloženja u brojnim područjima znanosti i tehnike, od izuzetnoga su značaja temeljna istraživanja tih procesa kao i međudjelovanja koja dovode do stvaranja taloga. Obzirom na činjenicu da su kalcijevi oksalati glavni sastojci mokraćnih kamenaca, njihovo izučavanje, kao i izučavanje fizikalno-kemijskih čimbenika koji dovode do njihovoga nastajanja jesu od posebnog značaja u području patološke mineralizacije. Kalcijevi oksalati tvore tri hidratna oblika od kojih je monohidrat (COM) termodinamički stabilan, dok su dihidrat (COD) i trihidrat (COT) metastabilni. Rezultate istraživanja utjecaja brojnih termodinamičkih i kinetičkih čimbenika, kao i potencijalnih inhibitora na nastajanje i transformaciju kalcijevih oksalata pri različitim eksperimentalnim uvjetima, prikazane u ovom pregledu, sadašnji su autori ostvarili i objavili tijekom 1980-ih.Precipitation from supersaturated solutions is in general affected by the physical chemical properties ot the solution, by the hydrodynamics of the system, i.e., by the processes of mixing reactants and stirring the system, as well as by soluble impurities present in the system. Therefore, such a knowledge should be considered in a number of areas where precipitation plays an important role. Since calcium oxalates have been found to be a major crystal constituent of urinary stones, their investigations, as well as investigations of physical chemical conditions relevant for their formation are of particular importance for fundamental research in the field of patological mineralization. Calcium oxalate forms three hydrates. These three hydrates are the thermodynamically stable monohydrate (COM) and the metastable modifications, dihydrate (COD) and trihydrate (COT). The results on investigations of the influence of a number of thermodynamic and kinetic factors, as well as the potential inhibitors, on the hydrate formation and transformation under different experimental conditions had been obtained and published by the present authors during 1980th

Formation and Morphology of Struvite and Newberyite in Aqueous Solutions at 25 and 37 °C

The influence of the initial reactant concentrations (ci(Mg)tot = 5.0 x 10–6 to 5.0 x 10–1 mol dm–3, ci(P)tot = ci(NH4)tot = 1.0 x 10–3 to 5.0 x 10–1 mol dm–3) and temperature (25 and 37 °C) on the composition and morphology of the precipitates formed in the system MgCl2-NH4H2PO4-NaOH-H2O at initial pHi = 7.40 has been investigated. Precipitation diagrams are presented showing the concentration regions within which different morphologies of solid phase have been formed. The solid phases aged for 24 hours were characterized by means of optical microscopy, FT-IR spectrophotometry, X-ray diffractometry and thermogravimetry. It was found that struvite was a predominant phase formed within the concentration region examined and newberyite was obtained only in the region where pH24h < 6.5. The influence of the initial pH on the formation and transformation of these two compounds were studied in the region 5.0 pHi ≤ 9.0 and the results are discussed

On Calcium Carbonates: from Fundamental Research to Application

Appearance of a solid phase from aqueous solution, known as precipitation, is responsible for the formation of numerous natural materials and technological products. Therefore, the knowledge on mechanisms of elementary processes involved in precipitation should be considered in the areas such as geology, oceanology, biomineralization, medicine, basic chemical and pharmaceutical industries, analytical and materials chemistry in particular. Calcium carbonates are a very suitable model system for investigations of these processes. Owing to their low solubility, a wide range of initial supersaturations can be achieved that direct to different conditions under which a particular process dominates. Calcium carbonates can precipitate in the form of six modifications (polymorphic or hydrated). In the Laboratory for Precipitation Processes, systematic investigations of the conditions for formation, crystal growth and transformation of amorphous calcium carbonate, calcium carbonate hexahydrate, calcium carbonate monohydrate, vaterite and calcite have been performed during the last nearly twenty years. An overview of these studies is presented

The Influence of a Protein Fragment Extracted from Abalone Shell Green Layer on the Precipitation of Calcium Carbonate Polymorphs in Aqueous Media

Many living organisms form mineral phases through biologically controlled processes, known as biomineralization. Thus created materials are composites of both, mineral and organic components. The shell of the gastropod mollusc red abalone (Haliotis rufescens) consists of calcite and aragonite layers, each of them containing characteristic biopolymers responsible for biomineralization. In this work, the effect of interstitial green sheet polypeptide, GP, extracted from the green layer of the mollusc red abalone shell, on the process of spontaneous precipitation of calcium carbonate polymorphs, was investigated. Three precipitation systems, in which the initial mineralogical composition of the precipitate was different, have been studied. Thus, in system (1) calcite appeared, in system (2) a mixture of calcite and vaterite was found, while in system (3), ASW, only aragonite precipitated. However, the precipitation kinetic measurements, X-ray diffraction, FT-IR spectroscopy, and light and scanning electron microscopy indicated that the addition of GP in the model systems caused the inhibition of precipitation and change of morphology of crystals as a consequence of GP adsorption on the crystal surfaces and its entrapment into the mineral structure. (doi: 10.5562/cca2197

Kinetic Approach to Biomineralization: Interactions of Synthetic Polypeptides with Calcium Carbonate Polymorphs

Biomineralization processes are the subject of numerous investigations. This article gives a review of the study on interactions between the charged polypeptides and the mineral surfaces involved in biomineralization, with an additional kinetic approach. The influence of polypeptides on two types of precipitation processes is discussed: the spontaneous precipitation from supersaturated solution and the growth kinetics of calcite seed crystals. In the first case the phenomenon of the formation and stabilization of metastable phases was found while in the second case the influence of the applied polypeptides on the kinetics and mechanisms of calcite crystal growth was investigated. Calcium carbonate polymorphs, calcite and vaterite, were used as biomineral substrates and acidic polypeptides, poly-L-aspartic (pAsp) acid and poly-L-glutamic (pGlu) acid, as simplified models of naturally occurring soluble acidic proteins. A basic polypeptide, poly-L-lysine (pLys), was also used in experiments in order to find out whether conformity between the crystal surface and the adsorbed polypeptide, or just the electrostatic interactions, have a decisive role in these processes. The addition of a particular polypeptide into the precipitation system caused a significant inhibition of nucleation and growth of vaterite, the extent of inhibition being in the order InhpAsp > InhpGlu >> InhpLys. In addition to the inhibition of precipitation, the change of the polymorphic composition and the crystal morphology of the precipitate were also achieved. The explanation of such acidic polypeptide behaviour is a consequence of kinetic constraints through the diverse efficiency of inhibition of both calcite nucleation and vaterite growth caused by adsorption of acidic polypeptides. The acidic polypeptides also caused the inhibition of calcite crystal growth, the effect being pAsp > pGlu, and changed the observed mechanism of growth controlled by the integration of ions into the spiral steps, as found for the model systems, to the surface nucleation rate-determining mechanism. Nonselective, weak and electrostatic adsorption of pLys at the crystal surface was probably responsible for increasing the calcite crystal growth rate when pLys was present at low concentrations and for inhibiting it at pLys higher concentrations. The strongest interactions between the crystal surfaces and the polypeptides, observed for the calcite/pAsp system, can account for coordinative interactions between the side chain carboxylic groups of the predominantly planar arrangement of the pAsp structure (β-pleated sheet) and Ca2+ ions from the crystal surface. (doi: 10.5562/cca1809

Precipitation Diagrams of Struvite and Dissolution Kinetics of Different Struvite Morphologies

Spontaneous precipitation in the systems MgCl2-H3P04-NH40H-NaCl (0.15 mol dm-3)-H20, MgS04-NH4H2P04-H20 and MgS04-NH4H2P04-NaCl (0.15 mol dm-3)-H20 was studied at 25 and 37 °C and initial pH = 4. Precipitates aged for 24 hours and 30 days were characterized by means of Chemical analyses, X-ray diffractometry, FT-IR spectroscopy and thermogravimetry. Struvite was found to be the predominant phase formed in a wide range of reactant concentrations. The thermodynamic solubility products of struvite, Ks° = c(Mg2+) · y2 · c(NH4+) · n · c(P043-) · y3, (pKs° = 13.359 ± 0.284 at 25 °C and pKs° = 13.269 ± 0.113 at 37 °C) were calculated from the final, equilibrium, pH values taking ali the relevant magnesium, phosphate and ammonium species into account. The dissolution kinetics of dendrites and rod-like crystals of struvite in water was followed by recording pH as a function of time and the linear dependence of the dissolution rate on the absolute undersaturation was found. The dissolution rate constants kdiss. were found to be 0.075, 0.103 and 0.152 dm3 mol-2/3 s-1 for rod-like crystals, and 0.331, 0.286 and 0.596 dm3 mol-2/3 s-1 for dendrites at 25, 30 and 37 °C, respectively. The activation energy for the dissolution of rod-like crystals was found to be (44.8 ± 1.1) kJ mol-1 and that for dendrites (37.6 ± 1.6) kJ mol-1. Analysis of the kinetic data suggests the diffusion of constituting ions away from the surface of the dissolving crystal or the desorption of ions from the crystal adsorption layer as the possible rate determining mechanisms of struvite dissolution