KCl Particles Research Articles

Surface chemistry features in the flotation of KCl

Despite the successful industrial practice to recover KCl by flotation, the adsorption state of collectors at KCl salt surfaces is still not fully understood. In this paper, the flotation behavior of KCl and NaCl using different collectors and captive bubble contact angle measurements at KCl and NaCl crystal surfaces in their saturated solutions are reported. The influence of collector concentration and collector structure is considered. The results show that both cationic and anionic collectors produce a hydrophobic state at the structure breaking KCl salt surface, with finite contact angle values of between 30 degrees and 60 degrees. In contrast, the contact angle at the structure making NaCl salt surface is zero at all collector concentrations, suggesting that no collector adsorption occurs, a supposition that is supported by results from molecular dynamics simulation (MDS). Further, it appears that the presence of surface defects such as edges and corners promote the adsorption of collectors at the KCl surface, and that the flotation is achieved by bubble attachment at the edges/corners of KCl particles with the formation of aeroflocs. (C) 2009 Elsevier Ltd. All rights reserved.

Deliquescence and Efflorescence of Potassium Salts Relevant to Biomass-Burning Aerosol Particles

Particles containing potassium salts are common in biomass burning plumes and include compounds such as KCl, KNO 3 , and K 2 SO 4 . We determined the deliquescence and efflorescence relative humidities of single- and multi-component potassium salts using an environmental transmission electron microscope and an environmental scanning electron microscope. KCl particles deliquesced at a relative humidity (RH) of 85% and effloresced at 56%. K 2 SO 4 particles deliquesced at 96% and effloresced at 60%. KNO 3 particles grew continuously with increasing humidity. If KNO 3 particles were heat-treated at 104°C overnight, they deliquesced at an RH above 90%. Atomized solutions of multi-component potassium compounds (KCl & KNO 3 and KCl & K 2 SO 4 ) formed particles that contained distinct grains of each compound upon drying. Particles formed from the KCl & KNO 3 mixtures grew continuously with increasing humidity until deliquescence occurred at an RH of 82% and efflorescence occurred at 58%. Particles from the KCl & K 2 SO 4 mixture began to take up water at an RH of 84%. They deliquesced at >90% and effloresced at 52%. This work provides new data for mixed aqueous electrolytes that are important for atmospheric science. Efflorescence values for K 2 SO 4 , KNO 3 , and internally mixed particles of K 2 SO 4 and KCl are reported here for the first time.

Microstructural investigation of the KCl-induced corrosion of the austenitic alloy Sanicro 28 (35Fe27Cr31Ni) at 600°C

High-temperature corrosion of stainless steel is important, particularly in bio-fuelled boiler applications. The flue gas is rich in water vapour and alkali salts, which accelerate the corrosion of the boiler material. The focus of this paper is on the breakdown of the protective oxide scale formed on Sanicro 28, which is a highly alloyed austenitic stainless steel (35Fe27Cr31Ni), in the presence of KCl(s). Laboratory exposures were carried out at 600°C in 5% O2+40% H2O for 1, 24 and 168 hours. The samples were coated with 0.10 mg/cm2 KCl prior to exposure and uncoated samples were exposed for reference. The aim was to link the observed mass gains and microstructure to oxidation mechanisms. The oxidized samples were analyzed by XRD, SEM/EDX, FIB and TEM/EDX. The exposures results in a very complex corrosion chemistry, including, e.g. the formation of potassium chromate and the rapid transport of iron species on the surface resulting in accumulation of oxide on the former KCl particles. However, the consumption of chromium and the presence of chloride on the surface does not result in the breakdown of the protective oxide. The ability of the alloy to withstand this harsh environment is tentatively attributed to the high Cr/Fe ratio.

The Influence of KCl on the Corrosion of an Austenitic Stainless Steel (304L) in Oxidizing Humid Conditions at 600 °C: A Microstructural Study

The effect of KCl on the corrosion behavior of the austenitic stainless steel 304L was studied at 600 °C in 5% O2 + 40% H2O + N2. The breakdown of the protective oxide was investigated. This was done through a detailed microstructural characterization of the oxide scales formed after 1, 24 and 168 h. The oxidized samples were investigated by SEM/EDX, FIB and STEM/EDX. The presence of KCl(s) causes a breakdown of most of the protective scale, even though it is not in direct contact with KCl(s) particles, starting after just 1 h exposure. A fast growing porous oxide formed in direct contact with (former) KCl(s) particles and an about 2 μm thick scale covered most of the surface. Only some regions were covered by a thin scale. K2CrO4 particles were randomly distributed all over the scale after 1 h exposure. The particles are situated above the oxide scale and are not in direct contact with the subjacent metal. The thin scale contains lower Cr levels than has been observed in corresponding scales formed in the absence of KCl. The breakdown of the protective scale is suggested to be caused primarily by the formation of K2CrO4, depleting the protective oxide in chromium. In addition, chromia evaporation contributes to chromia depletion and breakdown of the protective scale. Very little or no transition metal chlorides were found after breakaway oxidation. Cl is suggested to play a minor role in the initial breakdown of the protective scale. The presence of KCl particles caused local rapid oxidation, which results in an outward growing Fe and Fe–Cr rich porous oxide.

Precipitation of dodecyl amine in KCl–NaCl saturated brine and attachment of amine particles to KCl and NaCl surfaces

Long-chain amines, used in potash ore flotation as collectors, are insoluble in NaCl–KCl saturated brine. In commercial applications, these amines are melted at 70–90 °C, dispersed in acidic solution of hydrochloric or acetic acids, and such emulsions are then introduced to the flotation pulp. To model the commercial potash ore flotation process, dodecyl amine, used in this study, was melted at 70 °C, dispersed in hydrochloric acid aqueous solution and was added to a KCl–NaCl saturated brine at room temperature. This results in the precipitation of the amine. The present study summarizes the influence of the conditions on the particle size and morphology of the precipitating amine particles. Methyl isobutyl carbinol (MIBC), common frother in flotation processes, was shown to affect amine dispersion when added into a hot amine emulsion prior to mixing with a saturated brine. This study demonstrates that the precipitating amine particles are selectively abstracted by KCl particles, but not by NaCl particles.

Mid-Infrared Diffuse Reflection of a Strongly Absorbing Analyte on Non-Absorbing and Absorbing Matrices. Part II: Thin Liquid Layers on Powdered Substrates

The average total path length traveled by photons in mid-infrared diffuse reflection spectrometry of powdered potassium chloride matrices coated with a thin layer of silicone oil has been estimated. The average path length of the photons that had passed through the silicone oil layer was first calculated by the application of the Beer-Lambert law. The total path length through the coated particles was then estimated by dividing the path length of the silicone oil by its concentration. The average path length of the photons that had been diffusely reflected from KCl particles with an average diameter of approximately 5 microm that had been coated with a very thin layer of the silicone oil (corresponding to a concentration of 0.01% w:w) was estimated to be about 8 mm. This path length was significantly reduced either as the silicone oil concentration or the absorption of the matrix was increased. The result helps to explain why diffuse reflection spectrometry is a far poorer sampling technique for trace analysis when the matrix has strong absorption and why diffuse reflection is not a very promising technique for the standoff detection of nonvolatile chemical warfare agents.

Deactivation of V2O5-WO3-TiO2 SCR catalyst at biomass fired power plants: Elucidation of mechanisms by lab- and pilot-scale experiments

In this work, deactivation of a commercial type V2O5-WO3-TiO2 catalyst by aerosols of potassium compounds was investigated in two ways: (1) by exposing the catalyst in a lab-scale reactor to a layer of KCl particles or fly ash from biomass combustion; (2) by exposing full-length monolith catalysts to pure KCl or K2SO4 aerosols in a bench-scale reactor. Exposed samples were characterized by activity measurements, SEM-EDX, BET/Hg-porosimetry, and NH3 chemisorption. The work was carried out to support the interpretation of observations of a previous study in which catalysts were exposed on a full-scale biomass fired power plant and to reveal the mechanisms of catalyst deactivation.Slight deactivation (about 10%) was observed for catalyst plates exposed to a layer of KCl particles at 350°C for 2397h. No deactivation was found for catalyst plates exposed for 2970h to fly ash (consisting mainly of KCl and K2SO4) collected from an SCR pilot plant installed on a straw-fired power plant. A fast deactivation was observed for catalysts exposed to pure KCl or K2SO4 aerosols at 350°C in the bench-scale reactor. The deactivation rates for KCl aerosol and K2SO4 aerosol exposed catalysts were about 1% per day and 0.4% per day, respectively.SEM analysis of potassium-containing aerosol exposed catalysts revealed that the potassium salt partly deposited on the catalyst outer wall which may decrease the diffusion rate of NO and NH3 into the catalyst. However, potassium also penetrated into the catalyst wall and the average K/V ratios (0.5–0.75) in the catalyst structure are high enough to explain the level of deactivation observed. The catalyst capacity for NH3 chemisorption decreased as a function of exposure time, which reveals that Brønsted acid sites had reacted with potassium compounds and thereby rendered inactive in the catalytic cycle. The conclusion is that chemical poisoning of active sites is the dominating deactivation mechanism, but physical blocking of the surface area may also contribute to the loss of activity in a practical application. The results support the observation and mechanisms of deactivation of SCR catalysts in biomass fired systems proposed in a previous study [Y. Zheng, A.D. Jensen, J.E. Johnsson, Appl. Catal. B 60 (2005) 253].

Effects of high magnesium ion concentration on KCl flotation: Part II – Plant research

There appears to be several mechanisms affecting the recovery of coarse KCl particles as they flow through the flotation circuit of the Taquari Vassouras mine (Companhia Vale do Rio Doce; CVRD), Aracaju, Brazil in the presence of continually increasing concentrations of carnallite. The increase in carnallite assists in the deposition of fine NaCl and KCl crystals on the surface of the coarse KCl particles. The effect seems to be a slight net improvement in the surface hydrophobicity and therefore flotation recovery of the coarse KCl particles. As the concentration of Mg 2+ ions increase, the precipitation of fine crystals of NaCl and KCl starts to increase. These NaCl crystals appear to have fine inclusions of KCl on the surface (and vice versa) which appear to attract collector, thus reducing hydrophobicity and flotation recovery of the coarse KCl feed. It is at this stage that the removal of fine precipitates appears to become critical in order to provide enough collector coverage of the coarse KCl particles to keep them floating.

Effects of high Mg 2+ concentration on KCl flotation: Part I – Laboratory research

A series of flotation tests on coarse KCl particles in brine solution prepared from potash ore from the Taquari Vassouras mine (Companhia Vale do Rio Doce; CVRD), Aracaju, Brazil was carried out to determine the recovery of sylvite in the presence of high concentrations of Mg 2+. The introduction of Mg 2+ caused the precipitation of fine salt crystals that consist mostly of NaCl (90%+) but also some KCl. However, the introduction of Mg 2+ also caused the nucleation of fine crystals of NaCl and KCl on the surface of the coarse KCl in the flotation feed. The nucleation of these fine surface crystals on the coarse KCl may have added to a (net) improvement in the recovery of the coarse KCl. However, a precipitate of fine NaCl with some KCl crystals, competed for collector and caused depression of the coarse KCl. When these precipitates were removed before collector addition, the collector subsequently adsorbed on the coarse KCl and the recovery of coarse KCl improved significantly.

Influence of composition of KCl/silicate drilling fluids on rheological properties

The changes of the rheological parameters, such as apparent viscosity (µa), plastic viscosity (µp), dynamic yield stress (τ yd) and static yield stress (τ ys) with the proportion of KCl, silicate and bentonite were discussed. It is found that the acceptable values of µa, µp, τ yd and τ ys can be obtained when the mass ratio of bentonite, KCl and silicate is kept around 1:7:10. The effect of other factors, such as the particle size distribution of bentonite and zeta potential of clay, on the values of µa, µp, τyd and τys is also discussed. This discussion result could pave the way for better understanding of the subtle interaction between KCl, silicate and bentonite particles.

Formation and morphology of asymmetric NaCl particles precipitated at the liquid-liquid interface

Abstract —Asymmetric particles of NaCl and KCl crystals have been obtained by using a crystallization method. The particles were produced by precipitation at the solution-1-butanol interface. The two solvents are essentially immiscible, but have slight mutual diffusion. When the aqueous solution contacts with 1-butanol, the interfacial area becomes supersaturated, resulting in nucleation and particle growth in the interfacial zone. The asymmetric particles featured a stepped surface on the side in contact with 1-butanol. The other surfaces in contact with the aqueous phase were a flat cubic structure. Precipitated NaCl particles showed very clear asymmetric structure. However, some of KCl particles had less well-defined structures. This is due to the high diffusion rate of hydrated K ions and the fast diffusion results in a supersaturated state around the interface. This situation can be explained by a model of crystal growth based on solute clusters in supersaturated solutions.

Local reactions of KCl particles with iron, nickel and chromium surfaces

AbstractCorrosion of superheaters caused by the deposition and subsequent reaction of alkali chloride containing ashes is one of the main material problems by combustion of biomass for energy conversion. The alkali chloride particles are formed during combustion and transported as aerosol or in the vapor phase within the combustion gas, subsequently sticking on the surface of the metallic tube. The initial reaction between the tube surface and the salt particle plays a major role in the initiation of the corrosion process and, therefore, are studied in detail in this work. The salt particles were locally deposited by means of thermophoresis within an aerosol generator, available at MPIE. Studies on the reaction of KCl particles with iron surfaces showed that a reaction takes place already at 300 °C. In N2‐O2 atmospheres, the attack was very local, whereas the addition of 0.05 vol.% HCl to the reaction gas led to complete coverage of the iron surface with chloride. In contrast, reactions of KCl with nickel and chromium surfaces start to be significant only at 500 °C and higher. The paper summarizes the reaction behavior of Fe, Ni and Cr after thermophoretic deposition of KCl particles and subsequent reaction at elevated temperatures.

Local reactions between NaCl and KCl particles and metal surfaces

Local reactions of NaCl particles with pure iron surfaces have been investigated to compare with the results of previous studies on the local reactions of KCl particles. Before short-term oxidation at various temperatures in N2–20 vol.-%O2–0·05 vol.-%HCl atmospheres, microscale NaCl particles were deposited by thermophoresis on bare iron surfaces and pre-oxidised samples. After reaction, the samples were examined using field emission microscopy (FEM), X-ray photoelectron spectroscopy (XPS) and chemical analysis. In particular, NaCl particles reacted with the iron surface at 300°C, depending on the gas phase composition. In N2–O2 atmospheres very local reactions took place, whereas the addition of 500 vppm HCl led to complete coverage of the iron surface with chloride. In addition, the reactions of KCl particles on nickel surfaces at 500°C have been investigated for comparison with those of KCl and NaCl particles on iron surfaces at 300°C.

Experimental Studies of Heterogeneous Nucleation in the Turbulent Mixing Condensation Nuclei Counter

A method for varying the supersaturation in a turbulent mixing CNC has been used to examine heterogeneous nucleation of different compounds (working fluid) on various nuclei's compositions. Supersaturation was controlled by changing the vapor pressure of working fluid in nozzle flow, which was accomplished by saturating only a predetermined fraction of the flow while the keeping the total flow and temperature constant. This approach allows the partial pressure of the working fluid to be varied while maintaining a constant flow structure and temperature field. Experimental results characterizing the initial stages of heterogeneous nucleation are presented for NaCl, KCl, AgCl, and Ag particles. Heterogeneous nucleation was examined at various pressures of dibutylphthalate, octadecane, octadecanol, and octadecanoic acid. For octadecanoic acid as the working fluid, the size distribution of the grown particles is unimodal with the size increasing with increasing pressure of the working fluid. For the other working fluids, the initial size distribution splits into a bimodal distribution with one mode approximately the same as the initial distribution and a larger sized mode that grows with increasing pressure of the condensing vapor. For NaCl and octadecane and octadecanol, the initial unimodal size distribution splits into a trimodal size distribution.

SEM Investigation of Superheater Deposits from Biomass-Fired Boilers

Straw is used as fuel in relatively small-scale combined heat and power producing (CHP) grate boilers in Denmark. The large content of potassium and chlorine in straw greatly increases the deposit formation and corrosion of the superheater coils, compared to boilers firing coal. In this study, mature superheater deposit samples were extracted from two straw-fired boilers, Masnedø and Ensted, with fuel inputs of 33 MWth and 100 MWth, respectively. SEM (scanning electron microscopy) images and EDX (energy dispersive X-ray) analyses were performed on the deposit samples. Different strategies are adopted to minimize deposit problems at the two boilers. At Masnedø the final superheater steam temperature is 520 °C, no soot blowing of the superheaters is applied and a relatively large superheater area is used. At Ensted, an external wood-fired superheater is used in order to obtain a final steam temperature of 542 °C, while the steam exit temperature of the straw-fired boiler is 470 °C. The mature Masnedø deposit had a thickness of 2 to 15 centimeters and consisted of three distinct main layers. The thick intermediate layer was depleted in chlorine but rich in Si, K, and Ca. This Masnedø intermediate layer was probably generated by in-situ reaction between KCl and Si-rich ash particles, which leads to release of chlorine-containing gases. The innermost layer contained many sublayers of mainly iron oxide, KCl, and K2SO4. The Ensted deposit had a maximum thickness of a few centimeters. The intermediate Ensted layer consisted of melted KCl with inclusions of Ca- and Si-rich particles, and the innermost layer was an iron oxide next to a potassium sulfate layer. Compared to deposits formed on a probe during short-time experiments, the mature superheater deposits contained larger dense inner sublayers of pure KCl and K2SO4. The present study indicates that the innermost layer of the superheater deposits expands by condensation of KCl, even when the deposit has a thickness of several centimeters.

CVRD buys Mitsui shareholding in Caemi to gain 37% stake in Cadam

There appears to be several mechanisms affecting the recovery of coarse KCl particles as they flow through the flotation circuit of the Taquari Vassouras mine (Companhia Vale do Rio Doce; CVRD), Aracaju, Brazil in the presence of continually increasing concentrations of carnallite. The increase in carnallite assists in the deposition of fine NaCl and KCl crystals on the surface of the coarse KCl particles. The effect seems to be a slight net improvement in the surface hydrophobicity and therefore flotation recovery of the coarse KCl particles. As the concentration of Mg2+ ions increase, the precipitation of fine crystals of NaCl and KCl starts to increase. These NaCl crystals appear to have fine inclusions of KCl on the surface (and vice versa) which appear to attract collector, thus reducing hydrophobicity and flotation recovery of the coarse KCl feed. It is at this stage that the removal of fine precipitates appears to become critical in order to provide enough collector coverage of the coarse KCl particles to keep them floating.

Individual aerosol particles from biomass burning in southern Africa: 2, Compositions and aging of inorganic particles

Individual aerosol particles collected over southern Africa during the SAFARI 2000 field study were studied using transmission electron microscopy and field‐emission scanning electron microscopy. The sizes, shapes, compositions, mixing states, surface coatings, and relative abundances of aerosol particles from biomass burning, in boundary layer hazes, and in the free troposphere were compared, with emphasis on aging and reactions of inorganic smoke particles. Potassium salts and organic particles were the predominant species in the smoke, and most were internally mixed. More KCl particles occur in young smoke, whereas more K2SO4and KNO3particles were present in aged smoke. This change indicates that with the aging of the smoke, KCl particles from the fires were converted to K2SO4and KNO3through reactions with sulfur‐ and nitrogen‐bearing species from biomass burning as well as other sources. More soot was present in smoke from flaming grass fires than bush and wood fires, probably due to the predominance of flaming combustion in grass fires. The high abundance of organic particles and soluble salts can affect the hygroscopic properties of biomass‐burning aerosols and therefore influence their role as cloud condensation nuclei. Particles from biomass burning were important constituents of the regional hazes.

Particle sizing in dense, rapidly flowing KCI suspensions by photon migration techniques

AbstractThe first experimental measurement of particle‐size distribution (PSD) from undiluted, rapidly flowing potassium chloride (KCl) suspensions using continuous‐wave photon migration techniques is presented. PSDs were obtained from a laboratory simulation of production‐line slurries used in the chemical fertilizer industry. Spectral measurements of concentrated, rapidly flowing slurry containing 25–40% KCl particles were used to calculate the suspensions' reduced scattering coefficient and PSD using inverse algorithms. Our PSD results agree excellently with sieving measurements. Refractive index is important in the calculations of the PSD and the suspensions' reduced scattering coefficient.

Development of Titanium Coatings on Particulate Diamond

The performance of many wear‐resistant materials can be improved further by incorporating diamond into the structure. Diamond that has been coated with titanium is known to adhere well to the matrix particles and also prevents reaction with H2, which often is used in the sintering atmosphere. Two coating methods of coating diamond with titanium have been explored in this study: a sputtering method and a procedure that involves heating the diamond in a mixture of salt and titanium. The latter, which uses a salt mix of NaCl, KCl, and CaCl2 and metallic titanium particles 3 μm in size, heated at a temperature of 750°C in an argon atmosphere, is determined to be the best method.

COLLECTION OF FUNGAL SPORES ON AIR FILTERS AND SPORE REENTRAINMENT FROM FILTERS INTO AIR

The collection of fungal spores on ventilation filters and their potential for subsequent reentrainment were compared with the collection and reentrainment of standard test particles. Potassium chloride (KCl) particles were selected as the standard test particles, as recommended by the ASHRAE standard 52.2. Penicillium brevicompactum and Penicillium melinii were selected to represent common fungal spores in indoor air. Two commonly used filters were tested: medium-efficiency filter medium A from a prefilter and higher efficiency medium B from a fine filter. The collection efficiencies of filters were determined at a face velocity to the pleated filter assembly of 2.54 m s −1 , which is typical for both filters. The collection efficiency was found to be slightly lower for fungal spores than for KCl particles of the same aerodynamic size. When the reentrainment velocity was the same as the loading velocity through the filter medium (0.56 m s −1 for A, 0.09 m s −1 for B), the reentrainment rate was less than 0.4%. When the reentrainment velocity was increased to 3.00 m s −1 , the reentrainment of fungal spores was higher than that of KCl particles: 2–6% for P. brevicompactum, 5–12% for P. melinii, and 0.2–0.6% for KCl particles. The differences in behaviour between fungal spores and KCl particles were attributed to aggregation and deaggregation of fungal spores. The higher reentrainment rate of P. melinii compared to that of P. brevicompactum can be explained by the different surface structure of these spores. The results suggest that during the startup of a ventilation system or during other operations, when the air velocity may suddenly increase, reentrainment of fungal spores can be significant. Furthermore, if fungal spores grow on the ventilation filters, the reentrainment rate may become even higher than measured in this study.