Crystal Formation In Solutions Research Articles

Weathering of a mined quartz-carbonate, galena-sphalerite ore and release and transport of nanophase zinc carbonate in circumneutral drainage

The formation and transport of geogenic metal nanoparticles in mining-impacted environments is a developing concern because of their potential for greater distribution compared to larger particles. Discharge from the abandoned Gem Mine in the Coeur d'Alene Mining District of northern Idaho was examined for the presence of metal nanoparticles from weathering of an ore body of galena [PbS] and sphalerite [(Zn,Fe)S] with associated carbonate zones of siderite [FeCO3] and ankerite [Ca(Fe,Mg,Mn)(CO3)2] in intruded quartz veins. Analysis of this circumneutral discharge from the abandoned mine and groundwater in the receiving shallow aquifer indicate poor-quality mine drainage containing nanophase Zn-CO3 form(s) that dissociate into smaller particles or ions with release into the new geochemical environment of the aquifer. The nanoparticles were identified through acid titrations and dynamic light scattering analysis of 450-nm-filtered mine water. The stability of the nanoparticles was estimated through ζ potential analysis of mine water and groundwater, which indicated limited stability of the nanoparticles that was sufficient for transport in the mine drainage but insufficient for transport in the aquifer. The release of the nanophase Zn-CO3 form(s) likely occurs through weathering of secondary carbonate minerals in the mined areas of the Gem-Gold Hunter deposit through water-rock interaction → crystal repulsion → particle detachment → solution entrainment → and limited dissociation during transport as opposed to crystal formation in solution with mineral-phase saturation.

Molecular characterization of a prokaryotic polypeptide sequence that catalyzes Au crystal formation

The gold crystal-forming E. coli polypeptide sequence, MHGKTQATSGTIQS, is one of several polypeptide sequences that interacts with gold interfaces and catalyzes the formation of Au crystals in solution, with nucleated Au crystals preferentially featuring the (111) interface. To date, there have been no experimental studies which explore the structure of E. coli-expressed gold binding proteins or the binding of Au(III) ions by these polypeptides. In this present report, multidisciplinary approaches were applied to the 42-AA gold binding protein-1 (GBP-1/42) and to a model polypeptide representing the 14-AA integral repeat of this protein (GBP-1/14). CD and NMR spectroscopy indicate that neither the integral repeat nor the GBP-1 protein adopt folded structures in the apo form or in the presence of Au(III) ions; the integral repeat adopts a random coil-extended structure conformation [i.e., (MHGKTQA)random coil–(TSGTIQS)extended] and the GBP-1 protein appears to be similarly structured. These features are inconsistent with a templating structure. Mass spectrometry experiments indicate that the integral repeat binds up to two Au(III) ions per polypeptide molecule, and 1H NMR ROESY experiments pinpoint the interaction of Au(III) within two sites: the -QAT- region of the integral repeat MHGKTQATSGTIQS sequence, and, at the negatively charged C-terminus of this sequence. Collectively, our findings support the hypothesis that GBP-1 does not catalyze Au crystal formation via a templating mechanism; rather, the open, unfolded structure of this protein, combined with the presence of accessible proton donor/acceptor amino acids (Ser, Thr, Lys, Gln, His) most likely play a role in Au crystal formation in solution and may also explain the interactive nature of this polypeptide with Au interfaces.

Phenomena and mechanisms of mixed crystal formation in solutions II. Mechanism of interface processes

The characteristic features of formation of mixed crystals in solutions and the basic concept underlying these processes were established in [J. Crystal Growth. 255 (2003) 150; J. Crystal Growth. 172 (1996) 226; Zap. Vses. Mineral. O. (1983) 742; Zap. Vseross. Mineral. O. (1991) 3; Zh. Struct. Khim. (1994) 79]. The present study is a continuation of the complex research of morphology and defects of potassium acid phthalate−rubidium acid phthalate (KAP–RbAP) mixed crystals that are formed in aqueous solutions. The most important characteristic of this series is the formation of heteroepitaxial porous and continuous textures as a result of the exchange reaction between the crystal and the “foreign” solution. The interaction of KAP and RbAP crystals with aqueous solutions saturated with RbAP and KAP, respectively, is studied. The corresponding processes were observed both in situ and ex situ with optical and atomic force microscopes. The results obtained were used to develop the theoretical model of formation of specific morphological textures in liquid-phase heteroepitaxy, including the textures formed in aqueous solutions of various salts.

Phenomena and mechanisms of mixed crystal formation in solutions I. General concept on the example of the system KHC 8H 4O 4–RbHC 8H 4O 4–H 2O

A comprehensive study of crystal morphology and imperfections in the isomorphic series potassium acid phthalate–rubidium acid phthalate (KAP–RbAP) in aqueous solutions was conducted using a general model of the processes of mixed crystal formation in solutions discussed earlier by the authors on experimental and theoretical basis. The system was chosen as a model to interpret basic processes. The utilization of both substances as well as their solid solutions was taken into account. Interaction between RbAP or KAP crystals and aqueous solutions saturated with either KAP or RbAP or both, in ratios varying from 10 to 90 wt% (the step was about 10 wt%), has been studied. All the processes were observed in situ and ex situ by optical microscopy and X-ray topography (Lang method). Solubilities of KAP and RbAP mixtures in water were determined and compositions of corresponding solid solutions were estimated for the isotherms 29°C and 39°C. These indicated a considerable convex curvature in concentration Schreinemakers diagrams. The main peculiarity of crystals is their having heteroepitaxial porous or uniform textures, which occur due to the secondary volume deficit or excess at the exchange reaction between a crystal and solution. In turn, the primary/secondary volume ratio depends on the solubilities of the components in the system (unconnected with the molar volumes of the substances) determined directly from Schreinemakers diagrams. The convexity of the KAP–RbAP solubility isotherms displays specific crystal formation in this system compared with features of Co–Ni Tutton salts whose isotherms have small curvatures. Firstly, this appeared as a shift from volume-deficit replacement toward volume-excess replacement. This resulted in non-uniform heteroepitaxial textures and sharp slowing down of the process at an intermediate stage. Phenomena occurring in such peculiar systems and interactions between the crystals and solutions of intermediate compositions have not been investigated before. The results obtained became a basis for developing a theory of mixed crystal formation in solutions. Optically transparent mixed monocrystals containing about 3 and 5–10 wt% RbAP were isolated from solutions having the KAP/RbAP ratios of components 90/10 and 80/20 wt%.

Formation of crystals in solutions

Abstract Growth of high quality crystals has played an important role in sophisticated, modern- day technologies and in recent advances in physics. It has also provided examples in the study of self-organizing dissipative structures. This paper reviews the science of crystal growth and discusses recent data, particularly with regard to kinetics of growth and defects in crystal lattices.