Sawdust: A green and economical sorbent for thallium removal

Removal/preconcentration of thallium(I) ions from aqueous solution by sawdust; a waste material derived from the commercial processing of Cedrus Deodar wood for furniture production was investigated. A simple and low-cost modification results in increasing the sorption capacity of raw sawdust from 2.71 to 13.18 mg g⁻¹. Sorption was found to be rapid (98% within 8 min). The binding of metal ions was found to be pH dependent, optimal sorption accruing at around pH 6–9. Potentiometeric titrations of sawdust revealed two distinct pK_a values, the first having the value similar to carboxylic groups (3.3–4.8) and second comparable with that of amines (8.53–10.2) with the surface site densities of 1.99 × 10⁻⁴ and 7.94 × 10⁻⁵ mol g⁻¹, respectively. Retained Tl(I) ions were eluted with 5 ml 0.1 mol l⁻¹ HCl. Detection limit of 0.0125 μg ml⁻¹ was achieved with an enrichment factor of 160. Recovery was quantitative using sample volume of 800 ml. The Langmuir, Freundlich and D–R isotherm equations were used to describe partitioning behavior for the system at different temperatures. Kinetic and thermodynamic behavior of sawdust for Tl(I) ions removal was also studied.     

Shape-controlled multi-porous carbon with hierarchical micro–meso-macro pores synthesized by flash heating of wood biomass

We developed a simple synthesis of shape-controlled porous carbon materials that combine a high porosity of over 80% with a high Brunauer–Emmett–Teller surface area of 670 m²/g. The synthesis involves flash heating of sawdust and subsequent low-temperature heat treatment (380 °C). Flash heating changed the morphology of the sawdust to the specific three-dimensional microtexture of amorphous carbon, and the subsequent heat treatment dramatically increased the surface area of the shape-controlled porous carbon materials. The products consisted of cross-linked carbon beams containing surface micro-pores (pore size < 2 nm) and meso-pores (5 nm < pore size < 50 nm). Moreover, macro-pores (5 μm < pore size < 50 μm) were found between the cross-linked carbon beams.     

Production of anorthite refractory insulating firebrick from mixtures of clay and recycled paper waste with sawdust addition

Production of porous anorthite refractory insulating firebricks from mixtures of two different clays (K244 clay and fireclay), recycled paper processing waste and sawdust addition are investigated. Suitability of alkali-containing-clay, low-alkali fireclay, pore-making paper waste and sawdust in the products was evaluated. Prepared slurry mixtures were shaped, dried and fired. Highly porous anorthite ceramics from the mixtures with up to 30% sawdust addition were successfully produced. Physical properties such as bulk density, apparent porosity, percent linear change were investigated as well as the mechanical strengths and thermal conductivity values of the samples. Thermal conductivities of the samples produced from fireclay and recycled paper waste decreased from 0.25 W/mK (1.12 g/cm³) to 0.13 W/mK (0.64 g/cm³) with decreasing density. Samples were stable at high temperatures up to 1100 °C, and their cold strength was sufficiently high. The porous anorthite ceramics produced in this study can be used for insulation in high temperature applications.     

Wet vibro-grinding of zircon with surfactants

Conclusions An investigation was carried out of the effect of various surfactants added during the wet vibrogrinding of zircon on the degree of dispersion of the powder and on the sintering of specimens molded from the powders. When added in proportions up to 0.2% all surfactants tested (naphthenate soap, Asidol, titanium soap, GKZh-94, GKZh-10, triethanolamine, and sugar) helped to reduce the time required to grind the zircon to a given fineness from 15–20 to 4 h, i.e., by a factor of about 2.5–4.It was found that the proportion of fine fractions and the specific surface of the powder influence the open porosity and apparent density of the fired specimens. It was confirmed that sintering to an open porosity below 1% can be achieved with powders containing at least 80% grains finer than 5 including at least 60% grains finer than 2 which corresponds to a powder with a specific surface of at least 12 m²/g.It was established that in wet vibro-grinding a relation exists between the amount of accumulated iron grindings, on the one hand, and the degree of dispersion of the ground material and the apparent density of the fired specimens, on the other. The amount of iron grindings can serve as an indirect indicator of the suitability of the ground zircon for the production of superhigh density refractories. When wet vibrogrinding zircon it is recommended that an additive be used in the form of 0.05–0.1% triethanolamine.Translated from Ogneupory, No. 6, pp. 38–44, June, 1977.     

The grinding method and additives as factors in the sintering of zircon

Conclusions It was shown that specimens with an open porosity below 3% can be produced from zircon wet-ground in a vibromill, treated with acid, and containing over 80% grains smaller than 10 including 60–70% grains smaller than 2; the density of the specimens is highest (porosity below 1%) when they are fired at 1500°C and contain a maximum of 0.8–1% TiO₂.Specimens prepared from dry-ground zircon can be sintered at 1500–1580°C to a porosity of 3–20%) depending on the composition and amount of additive and on the content of grindings of metallic iron.Translated from Ogneupory, No. 2, pp. 26–32, February, 1977.     

Electrochemical reduction of nitrates and nitrites in alkaline nuclear waste solutions

Sodium nitrate and nitrite are major components of alkaline nuclear waste streams and contribute to environmental release hazards. The electrochemical reduction of these materials to gaseous products has been studied in a synthetic waste mixture. The effects of electrode materials, cell design, and other experimental parameters have been investigated. Lead was found to be the best cathode material in terms of current efficiency for the reduction of nitrate and nitrite in the synthetic mix. The current efficiency for nitrite and nitrate removal is improved in divided cells due to the elimination of anodic oxidation of nitrite. Operation of the divided cells at high current densities (300–600 mA cm^–2) and high temperatures (80°C) provides more efficient reduction of nitrite and nitrate. Nearly complete reduction of nitrite and nitrate to nitrogen, ammonia, or nitrous oxide was demonstrated in 1000 h tests in a divided laboratory electrochemical flow cell using a lead cathode, Nafion® 417 cation exchange membrane, and oxygen evolving DSA® or platinum clad niobium anode at a current density of 500 mA cm^–2 and a temperature of 70° C. Greater than 99% of the nitrite and nitrate was removed from the synthetic waste mix batch in the 1000 h tests at an overall destruction efficiency of 55%. The process developed shows promise for treating large volumes of waste.     

Electrochemical treatment of human wastes in a packed bed reactor

There is an increasing interest in the use of electrochemical methods for dealing with pollution problems. This paper deals with the mass balance and the use of a packed bed reactor for the electrochemical incineration of human wastes. Parametric studies were carried out to determine the effect of: (i) anodic particle size, (ii) flow rate of faeces/urine mixture, (iii) height of packed bed, (iv) current density and (v) cathode to anode spacing arrangement, on the rate of oxidation of human waste. It is shown that particles of Ebonex (0.5–1.0 mm diam.) coated with a catalyst layer, comprising SnO₂/Sb₂O₃, a solution flow rate of 0.9–1.4 cm s^–1 through the packed bed based on the cross sectional area of the reactor, a bed height of 5–8 cm and a current density based on the geometric area of the particles of 5 mA cm^–2 comprise an optimum set of parameters for the scale-up of a packed-bed electrochemical reactor system. A preliminary design for the further scale up of the process is also described.     

The effect of fertiliser type and application rate on denitrification losses from cut grassland in Northern Ireland

Denitrification losses were measured using the acetylene inhibition technique adapted for a coring procedure. Two soils under a cut ryegrass sward were used. One soil was a freely-drained clay loam receiving under 900 mm rainfall annually, the other soil being a poorly-drained silty clay receiving over 1100 mm rainfall annually. Swards at each site received up to 300 kg N ha^–1 yr^–1 of calcium ammonium nitrate (CAN), urea or a new fertiliser mixture GRANUMS (30% ammonium nitrate, 30% urea, 10% ammonium sulphate, 30% dolomite). For both soils the rate of denitrification exceeded 0.1 kg N ha^–1 day^–1 only when the air-filled porosity of the soil was < 30% v/v and soil nitrate was > 2 mg N kg^–1 in the top 10cm of the profile and when soil temperature at 10 cm was > 4°C. When the soils dried such that their air-filled porosity was > 30% v/v, denitrification rates decreased to < 0.08 kg N ha^–1 day^–1. Highest rates (up to 3.7 kg N ha^–1 day^–1) were observed on the clay soil following application of 94 kg N ha^–1 CAN to soil near field capacity in early summer 1986. Losses from CAN were approximately 3 times those from urea for a given application. Denitrification losses from the GRANUMS treatment were, overall, intermediate between those from CAN and urea but the daily losses more closely resembled those from the CAN treatment. The impeded drainage on the clay soil, where soil moisture contents remained close to field capacity throughout the year, showed denitrification losses roughly 3 times those observed on the more freely drained clay-loam for any given treatment. Over a 12-month period, N losses arising from denitrification were 29.0 and 10.0 kg N ha^–1 for plots receiving 300 kg N ha^–1 CAN and urea, respectively, on the well drained clay-loam and 79.0 and 31.1 kg N ha^–1 respectively, for identical plots on the poorly drained clay soil. Annual denitrification losses from control plots were < 1 kg N ha^–1 on both soils.     

High-density fused-silica ceramics

Conclusions We investigated the conditions for obtaining high-density (with zero open porosity) ceramics from fused silica glass.We clarified the optimum conditions for slip casting which would enable us to obtain dense (porosity up to 9–11%) casting with a compressive strength of up to 900 kg/cm².We also showed the relationship between initial (surface) crystallization of the material and the temperature and firing time.We established the influence of original porosity of the castings on their sintering and crystallization. The strength properties of the materials are given.Translated from Ogneupory, No. 8, pp. 45–51, August, 1968.     

N relationship in a legume nonlegume association grown in an intercropping system

Sorghum grown in a mixture with legumes viz. groundnut, mungbean and cowpeas took up more N than sorghum grown as sole crop. In a mixture with mungbean the total N uptake by sorghum was 8.65 g m^–2, while with sole sorghum it was 6.79 g m^–2. The per cent N derived from fertilizer (% Ndff) was highest with sole sorghum and the lowest when grown in mixture with legumes. It is possible that sorghum derived part of the N from the soil pool enriched by concurrently grown legumes in the mixture.     

生物质与聚乳酸共热解行为及其动力学研究

Thermal decomposition of polylactic acid （PLA） was studied in the presence of pine wood sawdust （PS）, walnut shell （WS）, corncob （CC） in order to understand the pyrolytic behavior of these components occurring in waste. A thermogravimetric analyzer （TGA） was applied for monitoring the mass loss profiles under heating rate of 10℃·min^-1. Results obtained from this comprehensive investigation indicated that PLA was decomposed in the temperature range 300 -372℃, whereas the thermal degradation temperature of biomass is 183-462℃. The difference of mass loss （AW） between experimental and theoretical ones, calculated as algebraic sums of those from each separated component, is about 17%-46% at 300-400℃. These experimental results indicated a significant synergistic effect during PLA and biomass copyrolysis. Moreover, a kinetic analysis was performed to fit thermogravimetric data, the global processes being considered as one to two consecutive reactions. A reasonable fit to the experimental data was obtained for all materials and their blends.     

Experimental casting of multichamotte refractories from slip

Conclusions The possibility of casting refractories from multichamotte slip with a maximum moisture content of 15% has been investigated; a preliminary treatment of the slip under vacuum is recommended as well as a brief vibration of the gypsum molds within a certain period after pouring.The high rate of moisture loss and solidification of multichamotte slip castings allow production on an industrial scale.Multichamotte kaolin mixtures yield castings up to 100 × 80 × 80 mm which acquire the following properties after firing at 1470° C: bulk density –2.17–2.26 g/cm³; porosity –12 to 18%; compressive strength –420 to 800 kg/cm²; loss on ignition –2. 7 to 4. 3; total shrinkage in relation to the size of gypsum molds –4 to 5%.The casting process is of practical value for the manufacture of multichamotte products (including high-alumina refractories) since molding the latter by means of pressing is either impossible or extremely difficult.Industrial tests are conducted for the verification and more accurate determination of technological parameters and the technical and economic effectiveness of the method.     

Removal of toxic metal Cr(VI) from aqueous solutions using sawdust as adsorbent: Equilibrium, kinetics and regeneration studies

In the present study, a low-cost adsorbent is developed from the naturally and abundantly available sawdust which is biodegradable. The removal capacity of Cr(VI) from aqueous solutions and from the synthetically prepared industrial effluent of electroplating and tannery industries is obtained. The batch experiments are carried out to investigate the effect of the significant process parameters such as initial pH, change in pH during adsorption, contact time, adsorbent amount, and the initial Cr(VI) concentration. The maximum adsorption of Cr(VI) on sawdust is obtained at an initial pH value of 1. The value of pH increases with increase in contact time and initial Cr(VI) concentration. The equilibrium data for the adsorption of Cr(VI) on sawdust is tested with various adsorption isotherm models such as Langmuir, Freundlich, Redlich–Peterson, Koble–Corrigan, Tempkin, Dubinin–Radushkevich and Generalized equation. The Langmuir isotherm model is found to be the most suitable one for the Cr(VI) adsorption using sawdust and the maximum adsorption capacity obtained is 41.5 mg g⁻¹ at a pH value of 1. The adsorption process follows the second-order kinetics and the corresponding rate constants are obtained. Desorption of Cr(VI) from sawdust using acid and base treatment exhibited a higher desorption efficiency by more than 95%. A feasible solution is proposed, for the disposal of the contaminant (acid and base solutions) containing high concentration of Cr(VI) obtained during the desorption process. The interference of other ions which are generally present in the electroplating and tannery industrial effluent streams on the Cr(VI) removal is investigated.     

Effect of Airflow Direction and Velocity on Smoldering Waves in Combustible Porous Layers

The mechanisms of propagation of smoldering waves in porous layers of pine sawdust were studied experimentally for cocurrent and opposed airflows in closed (with one open butt–end) and semiclosed (with a flat free surface) systems. We investigated the shape of the smoldering front and the effects of the airflow direction and velocity, combustible-layer porosity, and the dispersity of the sawdust layer on the smoldering wave velocity. Maximum temperature in the smoldering wave is established. In a closed system with airflow velocity higher than 5–7 cm/sec, the smoldering rate is an order of magnitude higher in a cocurrent flow than in an opposed flow. For cocurrent flow, the velocity of a smoldering wave is two orders of magnitude higher in a closed system than in a semiclosed system. The experimental dependences are explained. Key words: smoldering, wave processes, porosity.     

Micro- and macro-cellular sintered glass-ceramics from wastes

Glass obtained from melting a mixture of industrial wastes (panel glass from dismantled cathode ray tubes, mining residues from feldspar excavation and lime from fume abatement systems of the glass industry) has been employed for manufacturing micro- and macro-cellular sintered glass-ceramics. Micro-cellular glass-ceramics, with a closed porosity, were prepared by the direct foaming of the glass mass, determined by viscous flow sintering of fine powders (<37 μm), due to addition of a SiC-based waste (from the polishing of glass articles). The surface crystallization of glass, upon sintering, limited the porosity (being about 50%), but imparted a remarkable crushing strength to the products (up to about 80 MPa), useful for construction applications. Micro- and macro-cellular glass-ceramics, with an open porosity and very low relative density (from 40 to less than 10%), were prepared by the sintering of fine glass powders mixed with sacrificial poly-methyl methacrylate microbeads or deposited on sacrificial poly-urethane sponges. The crystallization, besides imparting a good mechanical strength, allowed the maintenance of the open-celled morphology, useful for filtering applications.     

Cathodic Decolourisation of Dyes in Concentrates from Nanofiltration and Printing Pastes

Direct cathodic reduction of dyes which contain an azo-goup in the chromophore was successfully used for decolourisation of intensively coloured concentrates from Nanofiltration treatment of textile effluents. Based on laboratory scale experiments, a technical multi-cathode electrolyser was applied for full scale decolourisation experiments at cell currents from 40 to 80 A. The absorbance of the treated wastes decreased from 60 to 80% of the initial value at an energy consumption of 2–8 kWh m^–3. Experiments with addition of redox mediator indicate a significant increase in decolourisation rate; however chemical consumption is increased for 0.5–1.5 kg m^–3 of waste. The decolourisation of reactive dye containing printing pastes was also achieved at the laboratory scale, where decolourisation of 60–80% was achieved.     

Graphitic mesoporous carbons synthesised through mesostructured silica templates

In this paper the fabrication and characterization of graphitizable and graphitized porous carbons with a well-developed mesoporosity is described. The synthetic route used to prepare the graphitizable carbons was: (a) the infiltration of the porosity of mesoporous silica with a solution containing the carbon precursor (i.e. poly-vinyl chloride, PVC), (b) the carbonisation of the silica–PVC composite and (c) the removal of the silica skeletal. Carbons obtained in this way have a certain graphitic order and a good electrical conductivity (0.3 S cm⁻¹), which is two orders larger than that of a non-graphitizable carbon. In addition, these materials have a high BET surface area (>900 m² g⁻¹), a large pore volume (>1 cm³ g⁻¹) and a bimodal porosity made up of mesopores. The pore structure of these carbons can be tailored as a function of the type of silica selected as template. Thus, whereas a graphitizable carbon with a well-ordered porosity is obtained from SBA-15 silica, a carbon with a wormhole pore structure results when MSU-1 silica is used as template. The heat treatment of a graphitizable carbon at a high temperature (2300 °C) allows it to be converted into a graphitized porous carbon with a relatively high BET surface area (260 m² g⁻¹) and a porosity made up of mesopores in the 2–15 nm range.     

Sintering of MgO made from MgCl2

Conclusions The production parameters for a densely sintered magnesite powders made from MgO obtained from the thermal decomposition of MgCl₂ have been established. It is shown that the mechanical activation of MgO can be carried out in a vibromill for 10–20 min with an addition of a surface-active material (distillery waste or C₇-C₉ (fatty acids).Under pilot-plant conditions, using the process which has been developed, we obtained an MgO briquette of apparent density 3.20–3.33 g/cm³, an open porosity of 1.6–4.6%, and a MgO concentration of 97.9%. The magnesite and magnesite-chrome articles based on this briquette have excellent properties.Deceased.Translated from Ogneupory, No. 7, pp. 41–45, July, 1979.     

Durability test of SOFC cathodes

The durability of solid oxide fuel cell (SOFC) composite cathodes of lanthanum strontium manganite and yttria stabilised zirconia was investigated. The cathodes were kept at constant, realistic operating conditions (–300 mA cm^–2 at 1000 °C in air) for up to 2000 h. After the 2000 h test the increase in electrode overvoltage exceeded 100% of the initial value. Nominally identical cathodes kept for 2000 h at 1000 °C in air without current load for comparison showed little or no degradation. Thus, the current load of –300 mA cm^–2, rather than the operation temperature of 1000 °C, was responsible for the degradation. Structural analysis showed an increase in the porosity at the electrode interfaces, when the electrode had been polarised. No such structural changes were found for electrodes tested without current load. The degradation is primarily ascribed to pore formation in the electrode material induced by an electric field.     

Use of cobalt-containing oxide waste for synthesizing enamels

It is shown that introduction of up to 7 wt.% cobalt-containing oxide catalyst waste into the mixture for synthesizing acid-resistant one-coat enamel does not worsen its wettability. The content of cobalt in such an enamel amounts to 0.2 – 0.3 wt.%, which is sufficient for its satisfactory cohesion with steel.Translated from Steklo i Keramika, No. 9, pp. 25 – 26, September, 1996.