Mirja Illikainen

Effect of grinding conditions in oscillatory ball milling on the morphology of particles and cellulose crystallinity of Norway spruce (Picea abies)

Abstract Norway spruce (Picea abies) has been submitted to oscillatory ball milling at room temperature and at -196°C. The effects of moisture content (MC) and cryogenic milling on the morphology and crystallinity of cellulose were investigated. At room temperature, MC had a significant effect on particle morphology and it was possible to produce powders of smaller particle size and rounder shape when the wood feed had a lower MC. Under cryogenic conditions, MC had less influence on the morphology, and the particle size was even smaller than that produced under ambient conditions. The degree of cellulose crystallinity in the milled wood was influenced by the MC of the feed, milling time, and milling temperature.

Partial Replacement of Portland-Composite Cement by Fluidized Bed Combustion Fly Ash

AbstractFly ash from fluidized bed combustion differs greatly from that of pulverized coal firing. The most noticeable differences are in morphology, reactivity, and chemical composition. The use o...

Effect of mild torrefaction on pulverization of Norway spruce (Picea abies) by oscillatory ball milling: particle morphology and cellulose crystallinity

Abstract The effects of mild torrefaction on the pulverization of Norway spruce sawdust have been studied. To this end, sawdust was dried and torrefied below 230°C for different periods of time to obtain samples with mass losses (ML) of 0.2%, 1.4%, and 2.8%, milled in an oscillatory ball mill, and the particle morphology and cellulose crystallinity of the powders were studied. The pretreatment leading to 0.2% ML had no effect on grindability, but that resulting in 1.4% ML improved grindability and a median particle size below 17.4±0.2 μm was attained. Torrefaction involving 2.8% ML reduced the specific energy consumption more than 21% when the targeted median particle size of the torrefied wood was between 18.7±0.5 and 79±3 μm. The mild torrefaction had a negligible influence on the aspect ratio distribution and cellulose crystallinity in the ball-milled wood.

Fly ash classification efficiency of electrostatic precipitators in fluidized bed combustion of peat, wood, and forest residues.

The increasing use of biomasses in the production of electricity and heat results in an increased amount of burning residue, fly ash which disposal is becoming more and more restricted and expensive. Therefore, there is a great interest in utilizing fly ashes instead of just disposing of it. This study aimed to establish whether the utilization of fly ash from the fluidized bed combustion of peat, wood, and forest residues can be improved by electrostatic precipitator separation of sulfate, chloride, and some detrimental metals. Classification selectivity calculations of electrostatic precipitators for three different fuel mixtures from two different power plants were performed by using Nelsons and Karniss selectivity indices. Results showed that all fly ashes behaved similarly in the electrostatic separation process SiO2 resulted in coarse fractions with Nelsons selectivity of 0.2 or more, while sulfate, chloride, and the studied detrimental metals (arsenic, cadmium, and lead) enriched into fine fractions with varying selectivity from 0.2 to 0.65. Overall, the results of this study suggest that it is possible to improve the utilization potential of fly ashes from fluidized bed combustion in concrete, fertilizer, and earth construction applications by using electrostatic precipitators for the fractionating of fly ashes in addition to their initial function of collecting fly ash particles from flue gases. The separation of the finer fractions (ESP 2 and 3) from ESP 1 field fly ash is recommended.

Morphological changes in never-dried kraft fibers under mechanical shearing

The modification of bleached never-dried cellulose fibers was studied under controlled compression and shearing conditions. Fibers were further treated in a high-intensity mixing device in low-consistency to determine if the fiber structure was weakened in the in-pad attrition. The difference between the development of the softwood and hardwood fibers was examined. The fiber properties were analyzed using a fiber morphology analyzer, fractional fiber analysis and an electron microscope. The results indicate that the shearing under the controlled compression at high consistency modified the softwood and hardwood fibers already at low-energy consumptions. The fiber length and width decreased, and the formation of curls and kinks was pronounced. However, the intensive mixing after in-pad attrition revealed that the fiber structure was not weakened under compression and shear forces; conversely, the fiber cell wall was more resistant for the intensive mixing. When comparing the results for hardwood and softwood fibers, the softwood fibers were more modified during in-pad attrition, whereas the fiber wall strengthening was more significant in the hardwood fibers.

Sonication-assisted surface modification method to expedite the water removal from cellulose nanofibers for use in nanopapers and paper making

This paper addresses the issue of high water retention by cellulose nanofibers (CNFs) that lead to exorbitant time consumption in the dewatering of CNF suspensions. This has been a bottleneck, which is restricting the commercialization of CNF derived products such as nanopapers and CNF reinforced paper sheets. As a remedy, we suggest an eco-friendly water-based approach that involves the use of sonication energy and lactic acid (LA) to modify the surface of CNFs. The suggested modification resulted in rapid water drainage, and dewatering was completed in 10 min; with unmodified CNFs, it took around 45 min. We have also compared the draining characteristics of LA modification of CNF suspensions with a common draining agent (NaCl); LA modification drains water 56% faster than the use of NaCl, and produced mechanically superior dimensionally stable nanopaper. Additionally, LA modification allows the addition of 10 wt.% CNF in paper sheets, with dewatering done in 2 min (while the unmodified CNFs took 23 min).

Utilization of Mineral Wools as Alkali-Activated Material Precursor

Mineral wools are the most common insulation materials in buildings worldwide. However, mineral wool waste is often considered unrecyclable because of its fibrous nature and low density. In this paper, rock wool (RW) and glass wool (GW) were studied as alkali-activated material precursors without any additional co-binders. Both mineral wools were pulverized by a vibratory disc mill in order to remove the fibrous nature of the material. The pulverized mineral wools were then alkali-activated with a sodium aluminate solution. Compressive strengths of up to 30.0 MPa and 48.7 MPa were measured for RW and GW, respectively, with high flexural strengths measured for both (20.1 MPa for RW and 13.2 MPa for GW). The resulting alkali-activated matrix was a composite-type in which partly-dissolved fibers were dispersed. In addition to the amorphous material, sodium aluminate silicate hydroxide hydrate and magnesium aluminum hydroxide carbonate phases were identified in the alkali-activated RW samples. The only crystalline phase in the GW samples was sodium aluminum silicate. The results of this study show that mineral wool is a very promising raw material for alkali activation.

Inertization of Mine Tailing via Cold Consolidation in Geopolymer Matrix

The consolidation via geopolymerisation is a room temperature alkaline chemical reaction of condensation between SiO2 and AlO2 monomers. Such a matrix can retain a large number of cations to compensate for the Al+3 in place of Si+4 in the tetrahedra. Arsenic-rich mine tailings from a gold mining site were activated with NaOH solution and commercial Na-Silicate (Na2O/SiO2 = 3) to produce a no-hazardous final material. Granulated blast furnace slag and metakaolin were used as co-binders to optimize the formulations. Leaching test was used to evaluate the inertization capability of the matrix after curing times of 7 and 28 days. The leaching results show that increasing curing time there is a significant decrease of As leaching due to the better consolidation of the material. Leaching of Cu, V, Ba and Zn significantly decrease, while Ni and Cr remain almost constant and Sb slightly increases.

Effect of Metakaolinite on Properties of Alkali Activated Slag Materials

Metakaolinite was introduced to alkali activated slag mortars and pastes. Properties of fresh and hardened mortars as well as phase composition and microstructure of hardened pastes were investigated. Introduction of metakaolinite both as addition as well as substitution of slag results in severe decrease in strength of the mortars. SEM observations revealed, that metakaolinite presence results in much less compacted microstructure comparing to reference slag paste. The reason for that are differences in phase composition as determined with XRD. C-S-H phase formation is retained in the presence of metakaolinite and thus degree of hydration of slag is decreased comparing to reference, slag paste.

Influence of Sulphides on Hydration of Ground Granulated Slag Alkali Activated Mortars and Pastes

Influence of sodium sulphide on properties of sodium hydroxide activated ground granulated blast furnace slag was investigated. Properties of both fresh (cone flow, density) as well as hardened (compressive strength) mortars were determined. Early hydration of pastes was investigated using conducting calorimetry. Results showed, that introduction of sodium sulphide to caustic soda activated slag only slightly influence the course of hydration process. Early strength is increased by about 10%. In later periods strength is virtually not affected by the presence of sodium sulphide. Those observations are confirmed by calorimetric results. Presence of sodium sulphide causes slight decrease in consistency of mortars. Colour of mortars is also affected by the presence of sulphides. It is more darker and it is most probably due to the reducing properties of sulphide ions. Results of model investigations on precipitated C-S-H phase showed, that presence of sulphides results in increased main basal spacing of C-S-H phase as determined by XRD.