Emil Makovicky

Pozzolanic reactions of six principal clay minerals: Activation, reactivity assessments and technological effects

Abstract Six standard clays, before and after calcination at 3 or 4 temperatures and being mixed with Ca(OH) 2 [CH] in the presence of simulated cement pore solution, and with ordinary Portland cement, respectively, were studied in detail. Chemical compositions of most clays conform well to the requirement in ASTM C 618. Water demand of clay-containing mortar varies, depending on the crystal chemistry of raw clays, and on the specific surface area of calcined clays. Measurements of XRD background or alkali soluble Si are rapid methods in evaluation of the pozzolanic activity of clays. Compressive strength of mortars based on the raw clays is affected by structure of clays. Calcination increases the pozzolanic activity of clays and the compressive strength of the Portland cement — clay mortars. A close correlation exists between compressive strength of mortars and particle size distribution of the dehydroxylated clays. The most common reaction products of clay — CH mixtures are C-S-H 2 and C 4 AH x , while C 2 ASH j8 and C 3 AH 6 were also detected with clays rich in Al.

Partitioning of nickel, copper, iridium, rhenium, platinum, and palladium between monosulfide solid solution and sulfide liquid: Effects of composition and temperature

Abstract Partitioning of Ni, Cu, and Pt-group elements (Ir, Rh, Pt, Pd) between monosulfide solid solution (Mss) and sulfide liquid has been investigated in the Fe-Ni-Cu-S system at 1000 and 1100°C and one atmosphere pressure. The Nernst partition coefficients (D = wt% in Mss/wt% in sulfide liquid) for Ni vary significantly from 0.19 to 1.17, while the values of DCu show a limited range of 0.17–0.27. The partition coefficients for Ir range from 1.06 to 13. Rhodium has a partition coefficient slightly lower than that of Ir under the same conditions, ranging from 0.37 to 8.23. The partition coefficients for Pt and Pd vary from 0.05 to 0.16, and from 0.08 to 0.27, respectively. The partition coefficients depend strongly on the bulk S contents of the system. They increase with increasing S contents in both Mss and liquid. Platinum, Pd, and Cu behave incompatibly during Mss crystallization, strongly partitioning into sulfide liquid. Nickel is incompatible in S-undersaturated systems and S-saturated systems. It becomes compatible when the system is S-oversaturated. Rhodium is compatible in S-saturated and S-oversaturated systems, but incompatible in S-undersaturated systems. Iridium changes from highly compatible through moderately compatible to slightly compatible when the system changes from S-oversaturated through S-saturated to S-undersaturated. The effect of temperature on metal partitioning is observed only in S-oversaturated systems, in which the partition coefficients for Ni and Rh increase with decrease of temperature. The compatible behavior of Ir and Rh, and incompatible behavior of Pt and Pd and Cu under S-saturated conditions appears to support the hypothesis that the observed metal zonation in many sulfide ore deposits such as Sudbury, Ontario and Norilsk, Siberia resulted from sulfide liquid fractionation.

Thermal stability and pozzolanic activity of calcined kaolin

Abstract Standard illite (American Clay Society, IMt-1) was calcined at 650,790 and 930°C for 100 minutes. Both the raw and calcined samples, before and after being mixed with Ca(OH) 2 in the presence of simulated cement pore solution, were studied by DTA, TG (for raw illite), XRD, SEM, EMPA and chemical solubility. The reaction rate of the mixtures was monitored by a chemical shrinkage test. Technological properties of the untreated and calcined illite-cement mortars were studied by theology (flow) and by a compressive strength test after reaction for 2, 7, 28 and 91 days. The current investigation revealed that illite has low pozzolanic activity. Dehydroxylation at 650°C does not upgrade it significantly. Further calcination at 790°C brings about considerable activation but it still does not qualify as a pozzolan. Calcination at 930°C produces the highest pozzolanic activity. Compressive strength of the mortar with 930°C illite is 79% of that of reference ordinary portland cement.

Binding of ethanol on calcite: the role of the OH bond and its relevance to biomineralization.

The interaction of OH-containing compounds with calcite, CaCO(3), such as is required for the processes that control biomineralization, has been investigated in a low-water solution. We used ethanol (EtOH) as a simple, model, OH-containing organic compound, and observed the strength of its adsorption on calcite relative to OH from water and the consequences of the differences in interaction on crystal growth and dissolution. A combination of atomic force microscopy (AFM) and molecular dynamics (MD) simulations showed that EtOH attachment on calcite is stronger than HOH binding and that the first adsorbed layer of ethanol is highly ordered. The strong ordering of the ethanol molecules has important implications for mineral growth and dissolution because it produces a hydrophobic layer. Ethanol ordering is disturbed along steps and at defect sites, providing a bridge from the bulk solution to the surface. The strong influence of calcite in structuring ethanol extends further into the liquid than expected from electrical double-layer theory. This suggests that in fluids where water activity is low, such as in biological systems optimized for biomineralization, organic molecules can control ion transport to and from the mineral surface, confining it to specific locations, thus providing the organism with control for biomineral morphology.

Experimental studies on the phase systems Fe-Ni-Pd-S and Fe-Pt-Pd-As-S applied to PGE deposits

SummaryIn the present paper current results of experimental investigation of the phase system Pd-Fe-Ni-S at 900°C, 725°C, 550°C and 400°C as well as of the phase system Pt-Fe-As-S at 850°C and 470°C are summarized. A preliminary note on the system Pt-Pd-As-S is added. Individual phase assemblages are presented, data on solubility of PGE in base metal sulphides/arsenides or alloys are given and solid solution ranges of important minerals are described as a function of temperature and phase assemblage. The extent and role of sulphide/arsenide melts in these systems are presented together with hints for, and examples of the application of the current experimental results for the explanation of ore-geological processes.ZusammenfassungIn der vorliegenden Arbeit werden bisherige Ergebnisse experimenteller Untersuchungen in den Phasensystemen Pd-Fe-Ni-S bei 900°C, 725°C, 550°C sowie 400°C, bzw. Pt-Fe-As-S bei 850°C und 470°C zusammengefasst. Vorläufige Anmerkungen zum System Pt-Pd-As-S werden gegeben. Die Phasenbeziehungen und die Löslichkeitsdaten von PGEs in Buntmetall-Sulfiden/Arseniden sowie deren Verbindungen werden präsentiert. Die Mischungsbereiche der wichtigsten Minerale werden als Funktion von Temperatur und Phasenvergesellschaftung diskutiert. Die Rolle von Sulfid/Arsenid Schmelzen in diesen Systemen und Beispiele für die Anwendung dieser experimentellen Ergebnisse zur Erklärung lagerstättenkundlicher Prozesse werden beschrieben.

Thermal stability and pozzolanic activity of raw and calcined mixed-layer mica/smectite

Abstract Samples of synthetic mixed-layer mica/smectite were calcined at 560°C, 760°C and 960°C. Chemical, physical and mineralogical properties of both untreated and calcined samples, before and after being mixed with Ca(OH) 2 in the presence of simulated cement pore solution, were studied in detail. Technological properties such as rheology and compressive strength of the clay mortars were also studied. The investigation indicates that the mixed-layer mica/smectite is a fairly good pozzolanic material and calcination is an effective approach to improve its pozzolanic activity. Dehydration and dehydroxylation of the sample at 560°C increase its pozzolanic activity considerably. Calcination from 560°C to 760°C does not cause further significant improvement, whereas calcination at 960°C again increases the compressive strength of the mortars to 113% (compared to the reference ordinary Portland cement (OPC) mortar). Most of six studied standard clay minerals are compositionally suitable to be used as pozzolanic materials. The common reaction products of clays and cement are CSH and C 4 AH x . The untreated clay minerals with stable layer structures have low pozzolanic activity and have negative effects on the compressive strength. Particle sizes of pozzolanic materials of calcined clay minerals and some other artificial pozzolans correlate well with the compressive strength of their cement mortars.

The role of Fe2+ and Fe3+ in synthetic Fe-substituted tetrahedrite

SummaryTetrahedrites with the composition between Cu12Sb4S13 and Cu10Fe2Sb4S13 were synthesized at 457 °C and 500 °C from the elements and carefully studied by Mössbauer spectroscopy of57Fe. Between Cu12Sb4S13 and Cu11Fe1Sb4S13 iron is predominantly ferric. Between Cu11Fe1Sb4S13 and Cu10Fe2Sb4S13 iron is predominantly ferrous and occupies the tetrahedral M1-sites.ZusammenfassungDie Rolle von Fe2+ und Fe3+ in synthetischen Tetraedriten mit Fe-Substitution Tetraedrite mit einer Zusammensetzung zwischen Cu12Sb4S13 and Cu10Fe2Sb4S13 wurden bei 457 °C und 500 °C aus den Elementen synthetisiert und sorgfdltig mit Mössbauer-Spektroskopie von57Fe untersucht. Zwischen Cu12Sb4S13 and Cu11Fe1Sb4S13 ist Eisen überwiegend dreiwertig. Zwischen Cu11Fe1Sb4S13 and Cu11Fe2Sb4S13 ist Eisen überwiegend zweiwertig und besetzt die tetraedrisch koordinierten M1-Plätze.

Thermal treatment and pozzolanic activity of Na- and Ca-montmorillonite

Abstract Samples of both untreated and calcined (at about 730, 830 and 930°C) Na- and Ca-montmorillonite, before and after having reacted with Ca(OH) 2 in the presence of simulated cement pore solution, were studied with XRD, SEM, EPMA and for chemical solubility. The reaction rate of the mixtures was monitored by a chemical shrinkage test. Technological properties of the (un) calcined montmorillonite-cement mortars were studied with theological properties and compressive strength tests after reaction for 2, 7, 28 and 91 days. The study indicates that the montmorillonites are fairly good pozzolanic materials and calcination substantially improves their pozzolanic activity. A clear optimum calcination temperature is 830°C for both Na- and Ca-montmorillonite.

Cyclically twinned sulphosalt structures and their approximate analogues

Two homologous series of cyclically twinned sulphosalt structures are defined in the present paper, with different atomic configurations around the site of sixand threefold axes. The zinckenite homologous series, M6+x+N(N+S) A12+N(N+7), contains zinckenite, a Pb-Sb sulphosalt, and sulphohalogenides of Bi and Pb. The Ba Bi sulphide homologous series, M12+x+N(N+S) A18+N(N+7), contains complex sulphides ofBi and alkaline earths. Degenerate (or approximate) cyclic twinning with only local threefold symmetry occurs in the structures of several Pb Bi Sb(Cu,Fe) sulphosalts and EU3Sb4Sg.The known and the missing members of these series are discussed and related hypothetical structures derived.

Another step toward understanding the true nature of sartorite: Determination and refinement of a ninefold superstructure

Abstract Single-crystal X-ray diffraction data, collected from a sartorite crystal from Lengenbach (Binntal, Valais, Switzerland), yielded a ninefold superstructure: space group P21/c; a = 37.71(2), b = 7.898(3), c = 20.106(8) Å, β = 101.993(7)°; R1 = 6.08% for 6293 reflections with I > 2σI. The sample is an N1,2 = 3,3 sartorite homologue and the refined formula Pb8Tl1.5As17.5S35 compares very well with the empirical formula Pb8.2Tl1.4As17.5Sb0.5S35 obtained from electron microprobe analyses. It has a high Tl content, up to 6.5 wt%. In a coupled substitution approximately 1.5 Tl+ replace about 0.5 As3+ and 1 PbS. The refined structure has 35 S atoms pfu instead of the expected 36 S (= 9 × 4 S, from PbAs2S4). The incorporation of substantial amounts of Tl+ into PbAs2S4 is essential for the type and periodicity of superstructures in sartorite. The refined superstructure can be interpreted as a socalled “lock-in” structure with a composition that yields a commensurate lattice for a mineral that usually has an incommensurate lattice. No commensurate periodicity could be found for a second crystal with about 0.5 Tl apfu.