Earth Construction and Landfill Disposal Options for Slaker Grits

Abstract: Slaker grits, an industrial residue originating from the chemical recovery process at sulfate (kraft) pulp mills, are typically disposed of to landfill in Finland. However, due to the relatively low total heavy metal and low leachable heavy metal, chloride, fluoride, sulfate, Dissolved Organic Carbon (DOC) and Total Dissolved Solids (TDS) concentrations, the residue is a potential earth construction material. This paper gives an overview of the relevant Finnish legislation on the use of industrial waste as an earth construction agent, the classification of waste into one of three classes: hazardous waste, non-hazardous waste and inert waste, as well as the broad waste policy goals under EU law that affects their management

Evaluation of trace element availability from secondary metallurgical slag generated in steelmaking by sequential chemical extraction

During carbon steel manufacture, slag residues are generated to remove material impurities from liquid metal and thus control the quality of carbon steel. As the utilization of secondary metallurgical slags is not as effi- cient as those of primary slags, a comprehensive charac- terization of steel ladle slag was performed. Pseudo-total concentrations of a wide range of elements were deter- mined during a 6-week sampling period with relevant physical and chemical properties, sequential extraction of trace elements, and parallel mineralogical characterization of extraction residues from a representative combined sample. According to the results, only Cr and V occurred in elevated concentrations with respective 6-week mean val- ues of 198 and 310 mg kg -1 (d.w.). The residual standard deviation of the weekly pseudo-total concentration values of the aforementioned elements (24 and 31 %, respec- tively) indicated that significant variation in the concen- tration of trace elements can occur due to fluctuation in process conditions and/or slag characteristics. The sequential extraction procedure suggested potential phyto- availability of V (123 mg kg -1 , d.w., amounting to 41 % of the respective pseudo-total concentration) through, e.g., changes in prevailing redox conditions. Although the analytical approach was validated by the analysis of a certified reference material and the calculation of extrac- tion recoveries, the mineralogical characterization of par- allel extraction residues indicated non-selectivity of the procedure coupled with potential redistribution phenomena during extraction with hydrogen peroxide and ammonium acetate

Removal of metals by sulphide precipitation using Na₂S and HS⁻-solution

Abstract Precipitation of metals as metal sulphides is a practical way to recover metals from mine water. Sulphide precipitation is useful since many metals are very sparingly soluble as sulphides. Precipitation is also pH dependent. This article investigates the precipitation of metals individually as sulphides and assesses which metals are precipitated as metal hydroxides by adjustment of the pH. The precipitation of different metals as sulphides was studied to determine the conditions under which the HS⁻ solution from the sulphate reduction reaction could be used for precipitation. H₂S gas and ionic HS⁻ produced during anaerobic treatment could be recycled from the process to precipitate metals in acidic mine drainage (AMD) prior to anaerobic treatment (Biological sulphate reduction), thereby recovering several metals. Precipitation of metals with HS⁻ was fast and produced fine precipitates. The pH of acid mine water is about 2–4, and it can be adjusted to pH 5.5 before sulphide precipitation, while the precipitation, on the other hand, requires a sulphide solution with pH at 8 and the sulphide in HS⁻ form. This prevents H₂S formation and mitigates the risk posed from the evaporation of toxic hydrogen sulphur gas. This is a lower increase than is required for hydroxide precipitation, in which pH is typically raised to approximately nine. After precipitation, metal concentrations ranged from 1 to 30 μg/L

Particle size distribution and dissolution properties of metals in cyclone fly ash

The particles in the examined cyclone fly ash were all smaller than 0.25 mm. in diameter, and particles smaller than 0.075 mm. in diameter accounted for 88.4 % of the ash weight. This result indicates that cyclone fly ash consists of particles with a small diameter. The metals in the cyclone fly ash were enriched in small particles. The highest concentrations for zinc, copper, lead, cadmium and molybdenum in the cyclone fly ash were found in the smallest particle size fraction (< 0.075 mm.) and for Barium, chromium, nickel, Vanadium and Cobalt in the second to smallest particle size fraction (0.0750.125 mm.). From an environmental and toxicological standpoint, the smallest particles are of the greatest concern when ash is handed at landfill disposal sites (transport and disposal especially in stormy weather conditions), and some studies have reported risks to workers from prolonged exposure to ash. The results of the comparison of various dissolution methods for metals showed that the digestion procedures with nitric acid alone (USEPA 3051) or with a mixture of nitric acid + hydrogen peroxide (USEPA 3050B) slightly underestimated the metal concentrations in the cyclone fly ash. Although the use of hydrofluoric acid is often necessary for the determination of a number of elements associated with siliceous minerals, its use can result in loss of trace elements during dissolution

The use of industrial waste materials for the simultaneous removal of ammonium nitrogen and phosphate from the anaerobic digestion reject water

Abstract The European Union’s circular economy strategy aims to increase the recycling and re-use of products and waste materials. According to the strategy, the use of industry waste materials and side flows is required to be more effective. In this research, a chemical precipitation method to simultaneously remove ammonium and phosphate from the reject water of anaerobic digestion plant using calcined paper mill sludge and fly ash as a precipitant, was tested. Paper mill sludge is a waste material formed in the paper-making process, and fly ash is another waste material formed in the power plant. Objective of this research was to test whether these industrial waste streams could be used as low cost precipitation chemicals for ammonium and phosphate removal from wastewaters and whether the precipitate could be suitable for fertilizer use. Results indicated that calcined paper mill sludge had high removal efficiency for both ammonium (97%) and phosphate (73%). Fly ash also had good removal efficiency for both ammonium nitrogen (74%) and phosphate (59%) at 20 ± 2 °C. The precipitates contained high concentrations of nitrogen and phosphate and could be used as a recycled fertilizer. Other possible mechanisms for the removal of phosphate and ammonium were considered

Cyclone processing of green liquor dregs (GLD) with results measured and interpreted by ICP-OES and NIR spectroscopy

An experimental design in cyclone drying parameters for green liquor sludge led to an efficient drying of the material and an interpretation of optimal cyclone parameters. The obtained dried materials were analyzed by ICP-OES and NIR spectroscopy. The inorganic analysis showed that a partial separation of toxic chemicals is possible and the NIR results could be used as an extra way of interpreting the results of the experimental design. The conclusion is that besides drying, also a change in chemical composition occurs as an effect of cyclone treatment. The NIR method is fast and requires little sample preparation while the ICP-OES method gives more direct inorganic results but is more demanding in time for sample handling and measurement.Peer reviewe