Waste Gypsum Research Articles

Performance of Ternary Binder Blend Containing Cement, Waste Gypsum Wall Boards and Blast Furnace Slag in CLSM

Controlled low strength materials (CLSM), is a self-flowing cementitious backfill material, most suitable for sustainability objectives since it makes use of wastes in large quantities. Wasted gypsum wall boards (drywalls), a construction & demolition waste, are known to pollute atmosphere by releasing harmful H2S gas when dumped at landfills. Use of waste drywalls with flyash, as cement replacement in concrete and CLSM, have resulted in low strength mixes at initial & later ages, respectively. In this paper powdered drywalls with ground granulated blast furnace slag (GGBS), was used as secondary cementitious material along with stone dust as fine aggregates, to produce sustainable CLSM mixtures with varying binder ratios and water contents. Reduction in compressive strength at later ages was not observed for mixes with low water contents, hence use of GGBS instead of flyash with lesser water contents, is effective in resisting detrimental effects of sulfates present in drywalls.

Synthesis of Calcium Ferrite from Waste Gypsum Board

Synthesis of Calcium Ferrite from Waste Gypsum Board

廃石こうボードを有効利用した晶析型脱リン材の作製

廃石こうボードを有効利用した晶析型脱リン材の作製

Determinação das propriedades físicas e mecânicas do gesso reciclado proveniente de chapas de gesso acartonado

Resumo A busca pela viabilidade técnica e econômica da reciclagem de resíduos na cadeia produtiva da construção civil vem atender às novas necessidades do setor de promover crescimento econômico integrado às necessidades sociais e ambientais. O crescente aumento do consumo das chapas de gesso acartonado carrega consigo o problema da geração dos resíduos de gesso, onde a falta de pesquisa e o descarte incorreto acaba destinando o resíduo gerado, na maioria das vezes, para aterros ou bota-foras irregulares, sem controle ou estimativa de volume. No presente trabalho, por meio da adoção de um processo de reciclagem composto das etapas de moagem e calcinação do resíduo das chapas de gesso acartonado, determinaram-se as propriedades físicas e mecânicas do gesso reciclado proveniente das chapas de gesso acartonado. A análise dos resultados mostrou a viabilidade da reciclagem, pois após a reidratação foi possível moldar corpos de prova, demonstrando que é possível reciclar um produto que hoje é descartado.

Investigation on gypsum plaster waste recycling: an eco-friendly material

Reducing the anthropogenic impacts on the environment is an important task, one that must be tackled in the building sector, which has considerable responsibility for such impacts. The amount of construction and demolition waste is increasing, and, consequently, so is gypsum plaster waste. This waste is due to the increase of using gypsum plaster in buildings as renderings and plates. This paper presents results that can enhance the value of gypsum waste recycling, thus reducing the damage the building sector does to the environment. Both the energy consumed in recycling and the way to recycle in stationary kilns were studied in order to establish the best calcination temperature and the residence time. With this result (calcination time and temperature), the properties of the recycled plaster were evaluated in powder, fresh state and hardened state. The results obtained are better than for commercial gypsum plaster, thus indicating that this a good way to recycle and add value to this waste material.

Mineral Carbonation of Phosphogypsum Waste for Production of Useful Carbonate and Sulfate Salts

Phosphogypsum (CaSO4·2H2O) waste is produced in large amounts during phosphoric acid (H3PO4) production. Minor quantities are utilized in construction or agriculture, while most of the material is stockpiled, creating an environmental challenge to prevent pollution of natural waters. In principle, the gypsum waste could be used to capture several hundred Mt of carbon dioxide (CO2). For example, when gypsum is converted to ammonium sulfate ((NH4)2SO4) with ammonia (NH3) and CO2, also solid calcium carbonate (CaCO3) is generated. The ammonium sulfate can be utilized as a fertilizer or in other mineral carbonation processes that use magnesium silicate-based rock as feedstock, while calcium carbonate has various uses as e.g. filler material. The reaction extent of the described process was studied by thermodynamic modeling and experimentally as a function of reactant concentrations and temperature. Other essential properties such as purity and quality of the solid products are also followed. Conversion efficiencies of >95% calcium from phosphogypsum to calcium carbonate are obtained. Scalenohedral, rhombohedral and prismatic calcite particles can be produced, though the precipitates contain certain contaminants such as rare earth metals and sulfur from the gypsum. A reverse osmosis membrane cartridge is also tested as an alternative and energy-efficient method of concentrating the ammonium sulfate salt solution instead of the traditional evaporation of the process solution.

Engineering properties of controlled low strength materials using flyash and waste gypsum wall boards

The discarded gypsum wallboards (drywalls) dumped at landfills, release hydrogen sulfide gas, a harmful substance, to the atmosphere along with the leachate at the landfill. In this paper, the discarded drywalls were utilized as secondary cementitious materials in controlled low strength materials (CLSM) with flyash and cement. Quarry dust, a stone industry waste was used as fine aggregates. CLSM mixes were produced for varying water contents, drywall and flyash to cement ratios by weight. Spread flow, Marsh flow time and fresh density properties at fresh state, and un-confined compressive strength, settlement and density properties at 3, 7, 28 and 56days for hardened state, were investigated. Reduced compressive strengths at later ages due to use of drywalls were observed. Flow and strength phenomenological models were generated using wide range of experimental data and validated for separate set of experimental data, to encourage production of CLSM using waste drywalls, of required parameters instead of conventional trial and error process.

An assessment of geo-environmental properties for utilization of recycled gypsum in earthwork projects

This paper presents an assessment of geo-environmental properties for the incorporation of recycled gypsum, produced from gypsum waste, as an additive material in earthwork projects. In this study, the solubility of Fluorine, Boron and hexavalent Chromium and the emission of hydrogen sulfide gas refer to geo-environmental properties. To achieve this objective, the tested soil was mixed with recycled gypsum in conjunction with lime and cement in different proportions to overcome the solubility of gypsum and to reduce the solubility of harmful substances. The results of the study show that the utilization of recycled gypsum alone, as an additive material for earthwork projects, has a negative effect on the emission of hydrogen sulfide, while the addition of a solidification agent, such as cement or lime, to the recycled gypsum reduced the emission of hydrogen sulfide gas. The suggested contents and ratios for the gypsum–cement and gypsum–lime admixtures used in this study are safe against the emission of hydrogen sulfide because their measurements were found to be below the standard limits. Increasing the proportion of cement or lime in a gypsum–soil mixture has a significant effect on the reduction in Fluorine solubility. The content of the admixture has a significant effect on the reduction in Fluorine solubility in the case of gypsum–cement, while there is not much difference in the measured values of Fluorine in the gypsum–lime admixture. The intensity of ettringite increases with the increase in admixture content and the decrease in the admixture ratio, while the intensity of calcite increases with increases in both the content and the ratio of the admixture. The formation of ettringite has a significant effect on the capture of Fluorine, namely, the solubility of Fluorine decreases with the increase in ettringite intensity. The measured values for the solubility of harmful substances, including Fluorine, Boron and hexavalent Chromium and the emission of hydrogen sulfide gas, were found to lie within the standards for the investigated limits of the gypsum–soil mixture treated with cement or lime in the present study. This proves that the utilization of recycled gypsum in conjunction with cement or lime, as a stabilizer material and within the investigated limits, is safe and meets the environmental standards.

Synthesis of high-purity precipitated calcium carbonate during the process of recovery of elemental sulphur from gypsum waste

We recently showed that the production of elemental sulphur and calcium carbonate (CaCO3) from gypsum waste by thermally reducing the waste into calcium sulphide (CaS) followed by its direct aqueous carbonation yielded low-grade carbonate products (i.e. <90mass% as CaCO3). In this study, we used the insight gained from our previous work and developed an indirect aqueous CaS carbonation process for the production of high-grade CaCO3 (i.e. >99mass% as CaCO3) or precipitated calcium carbonate (PCC). The process used an acid gas (H2S) to improve the aqueous dissolution of CaS, which is otherwise poorly soluble. The carbonate product was primarily calcite (99.5%) with traces of quartz (0.5%). Calcite was the only CaCO3 polymorph obtained; no vaterite or aragonite was detected. The product was made up of micron-size particles, which were further characterised by XRD, TGA, SEM, BET and true density. Results showed that about 0.37 ton of high-grade PCC can be produced from 1.0 ton of gypsum waste, and generates about 0.19 ton of residue, a reduction of 80% from original waste gypsum mass to mass of residue that needs to be discarded off. The use of gypsum waste as primary material in replacement of mined limestone for the production of PPC could alleviate waste disposal problems, along with converting significant volumes of waste materials into marketable commodities.

Sintering Behavior and Diametral Tensile Strength Properties of Hydroxyapatite-Zirconia Composites

. The aim of this study is to evaluate the sintering behavior and diametral tensile strength properties of hydroxyapatite-zirconia (HA-ZrO2) composites. HA powder were synthesized from gypsum waste with diammonium hydrogen phosphate (DHP) solution via microwave-precipitation treatment. HA mixed with various amounts of ZrO2 (0, 20, 30 and 40 wt.%) for six hours. HA-ZrO2 powder were molded in a metal die and pressed at 100 MPa. The green bodies were sintered for 2 hours at temperature 1450°C. Characterization of HA and HA-ZrO2 composites were conducted by XRD, XRF and SEM-EDX. The apparent porosity of HA-ZrO2 composites were measured using the Archimedes method. Diametral tensile strength testing of HA-ZrO2 composites were loaded at a crosshead speed of 5 mm/min. The results of the characterization of HA powder are the main (h k l) indices for HA are: (2 1 1), (2 0 2) and (0 0 2), Ca/P molar ratio is 1.71, level of purity is 88.68 %. The main (h k l) indices for HA-ZrO2 composites are: (2 2 0), (0 2 10) and (2 0 20). Porosity of HA-ZrO2 composites values in the range of 39.59-19.82%. Diametral tensile strength of HA-ZrO2 composites increased from 4.96 to 7.77 MPa when amounts of ZrO2 increased up to 40 wt%. This phenomenon is caused by porosity decrease and crack deflection.

Review on the effect of gypsum content on soil behavior

Abstract Increasing the utilization of urban soil usage brings along very important problems to be addressed at the international level regarding the use of sulfate bearing soils as construction materials. After briefly exploring current research perspective, this paper captures the current state of the art in the field of sulfate bearing soils used as construction materials through a detailed discussion of different studies that pave the way to the possible treatment of such soils to be used in road construction. Additionally, the purpose of this paper is to acquaint geotechnical and pavement engineers with the present state of the art of the physical and chemical properties of gypsum and hence its effect on the subgrade soil performance. On the other hand, this paper discussed an opposite action in which some researchers have mixed recycled waste gypsum components with soil in order to stabilize it. In other words, a number of open research issues are highlighted with the intension of inspiring new conditions and developments in stabilizing problematic gypsiferous soil as well as adding gypsum to stabilize non gypsiferous soils of weak performance.

Thermochemical reduction of pelletized gypsum mixed with carbonaceous reductants

The recovery of better quality waste gypsum during acid mine drainage (AMD) neutralization is one step closer to achieving downstream waste gypsum beneficiation for recovery of valuable materials. This can facilitate recovery of treatment costs and prevention of environmental pollution from gypsum waste-dumps. Thermal reduction using rotary kilns to recover valuable materials from waste gypsum remains a critical and controversial process because of waste gypsum handling problems, environmental pollution due to dust and gaseous emissions and poor conversion yields. In order to mitigate these problems and improve waste gypsum conversion yields, pelletization of waste gypsum in the presence of binders (starch and cellulose) was investigated. A laboratory-scale disc pelletizer was used to produce pellets from a mixture of coal and commercial gypsum or waste gypsum, generated during AMD neutralization, with starch and micro-crystalline cellulose used as binders. The pellets were subjected to high-temperature thermal treatment in a tube furnace to generate calcium sulphide (CaS), an important intermediate for waste gypsum beneficiation. The kinetics of thermal conversion of pelletized waste gypsum to CaS were found to be highly dependent on furnace temperature. Results also showed that pelletization affords improved handling of waste gypsum while use of binders as additives significantly improved the CaS yield, with starch giving the better yield compared to cellulose.

On the compressive strength and geo-environmental properties of MC-clay soil treated with recycled bassanite

The use of recycled bassanite, produced from gypsum wastes, in ground improvement projects is initiated recently in Japan to eliminate the huge quantities of gypsum wastes. Meanwhile the use of recycled bassanite has a positive effect on the environment and economy, it has many challenges. These challenges are related to the release of fluorine more than the standard limits results in contaminated fluorine soil. This research investigates the effect of the amount of bassanite, and water content on the release of fluorine from MC-clay soil stabilized with bassanite, taking in consideration their effect on the compressive strength. Recycled bassanite was mixed with furnace cement with a ratio of 1:1 to prevent the solubility of bassanite. Different amounts of this admixture were mixed with the tested soil at different water contents. Unconfined compression test was used to determine the compressive strength while the solubility of fluorine was used to represent the geoenvironmental properties in term of the release of fluorine. Scan electron microscopic (SEM) test was done to identify the development of cementation compounds in the matrix of treated-bassanite soil. Test results showed that, the addition of bassanite had a significant effect on the improvement of compressive strength by increasing the amount of bassanite. Curing time had a significant effect on the increase of compressive strength, the strength increases with the increase of curing time, especially in the later curing time. The release of fluorine increases with increasing the amount of bassanite in soil mixture. The increase of water content had an indirect effect on the release of fluorine while it had a negative effect on the improvement of strength and consuming the amount of admixture. The increase of strength is associated with the decrease of the release of fluorine. Recycled bassanite, produced from gypsum wastes, had a potential to be used as a stabilizer material for MC-clay soil and meet the standards of environment.

Waste Gypsum Board and Ash-Related Problems during Combustion of Biomass. 1. Fluidized Bed

This paper is the first in a series of two describing the use of waste gypsum boards as an additive during combustion of biomass. This paper focuses on experiments performed in a bench-scale bubbling fluidized-bed reactor (5 kW). Three biomass fuels were used, i.e., wheat straw (WS), reed canary grass (RC), and spruce bark (SB), with and without addition of shredded waste gypsum board (SWGB). The objective of this work was to determine the effect of SWGB addition on biomass ash transformation reactions during fluidized bed combustion. The combustion was carried out in a bed of quartz sand at 800 or 700 °C for 8 h. After the combustion stage, a controlled fluidized–bed agglomeration test was carried out to determine the defluidization temperature. During combustion experiments, outlet gas composition was continuously measured by means of Fourier transform infrared spectroscopy. At the same place in the flue gas channel, particulate matter was collected with a 13-stage Dekati low-pressure impactor. Bottom and cyclone fly ash samples were collected after the combustion tests. In addition, during the combustion tests a 6-h deposit sample was collected with an air-cooled (430 °C) probe. All ash samples were analyzed by means of scanning electron microscopy combined with energy dispersive X-ray spectrometry for elemental composition and with X-ray powder diffraction for the detection of crystalline phases. Decomposition of CaSO4 originating from SWGB was mainly observed during combustion of reed canary grass at 800 °C. The decomposition was observed as doubled SO2 emissions. No significant increase of SO2 during combustion of SB and WS was observed. However, the interaction of SWGB particles with WS and SB ash forming matter, mainly potassium containing compounds, led to the formation of K2Ca2(SO4)3.

Comparative life cycle assessment of plasma-based and traditional exhaust gas treatment technologies

The emissions of airborne contaminants from various industrial processes are an important source of air pollution and presents problems for human health and the environment in general. The removal of gaseous pollutants, such of nitrogen and sulphur oxides (NOx and SOx), from exhaust gases, or volatile organic compounds (VOC) emitted from various industrial processes is of continuous challenge in the environmental engineering. Plasma-based pollutant decomposition methods emerge as promising techniques, but little is known about their overall environmental performance. We compared two plasma based technologies (Electron Beam Flue Gas Treatment (EBFGT) and Dielectric Barrier Discharge (DBD) against the conventional methods (Wet Flue Gas Desulphurization with Selective Catalytic Reduction, WFGD+SCR, biofiltration and adsorption) using life cycle analysis (LCA), which took into account the usage of materials, waste generation and energy consumption. Five main categories (Global Warming, Ozone Layer Depletion, Acidification, Euthrophication and Human Toxicity, based on the CML2001 method) were used for the environmental impact evaluation. Based on CML2001 IKP Experts weighting, WFGD+SCR technology is marginally more environmentally friendly in comparison to EBFGT (59.25 to 73.74 CML2001 IKP Experts score). The generation of byproducts (in this case gypsum waste) is the main disadvantage of the WFGD+SCR. At the same time, EBFGT enables formation of useful byproducts, which are suitable to be utilized as fertilizers in the agriculture sector. On the other hand, DBD was six times more favorable to the environment than the adsorbtion and more than two times more environmentally friendly than the biofiltration technology (4.23, 27.78 and 9.29 relative units, respectively). With respect to the adsorption/thermal incineration of VOCs, both the electricity and the material consumption, as well as the management of byproducts caused the highest impact. In case of biofiltration, the management of remaining filter material waste (in this case, landfilling) was the most significant. Relatively high electrical energy demand causes lower positioning of plasma based technologies in cases where no other materials are utilized and major waste is formed. In turn, many traditional end-of pipe technologies are associated with high amounts of process waste, which provides plasma technologies with an opportunity to establish them in the market as more efficient and in many occasions, more environment-friendly ones.

Making sense of our mining wastes: Removal of heavy metals from AMD using sulphidation media derived from waste gypsum

') ;:?: This study investigates the recovery of water and THE selective removal of valuable metals from acid mine drainage (AMD) using sulphidation media (CaS) derived from waste gypsum. AMD systems containing Fe(II), Ni, Co, Zn, and Pb were investigated using CaS produced from the carbothermal reduction of Anglo Coal waste gypsum at 1025°C to precipitate metals as insoluble metal sulphides. The results show a sulphidation dependence on the pH, sulphide dosage, and metal concentration. The selective sulphidation of metals also showed significant dependence on the respective metal sulphide solubility order as a function of pH. According to the Department of Environmental Affairs’ South African Waste Information Centre, over 42 million cubic metres of general waste is generated every year in South Africa and mining waste is by far the biggest contributor to the solid waste (about 72%)). Although alarming, these vast quantities of waste also present an opportunity for integrated economic development, particularly in the recycling sector. The major argument has always been that the mining sector generates a large number of waste streams which show strong differences in time, in their treatment methodologies, or even in their spatial distribution. This paper presents a case of a simple strategy for integrated recycling of two mining waste streams and highlights the need for the mining industry to break away from the traditional ‘linear’ cul-de-sac disposal of wastes and think of new sustainable ways of waste management.

廃石膏ボードを利用したカルシウムフェライトの製造

廃石膏ボードを利用したカルシウムフェライトの製造

MICROBIAL LEACHING OF CHROMIUM FROM SOLIDIFIED WASTE FORMS – A KINETIC STUDY

In this study, Thiobacillus thiooxidans (T. thiooxidans) was used to study the microbial stability / degradation of cement-based waste forms. The waste forms contained a chromium salt (CrCl3·6H2O), cement and other additives viz., lime and gypsum in two different proportions. The experimental samples of all the simulated waste forms showed evidence of microbial growth as indicated by substantial increase in sulfate. Chromium leached from the waste forms was found to be lowest in cement – lime solidified waste forms (0.061 mg·l-1) and highest in cement gypsum waste forms (0.22 mg·l-1) after 30 days of exposure. These values were lower than the toxicity characteristic leaching procedure (TCLP), regulatory limit (5 mg·l-1). Model equations based on two shrinking core models (acid dissolution and bulk diffusion model), were used to analyze the kinetics of microbial degradation of cement based waste forms. The bulk diffusion model was observed to fit the data better than the acid dissolution model, as indicated by good correlation coefficients

Compressive strength and microstructure of soft clay soil stabilized with recycled bassanite

This paper investigates the microstructure and mineralogical compositions of soft clay soil stabilized with bassanite that is produced from gypsum waste materials. Bassanite was mixed in different ratios with cement and lime, as a solidification agent, to prevent the solubility of bassanite. Different amounts of these admixtures were mixed with the tested soil. Scan electron microscopic (SEM) and X-ray diffraction (XRD) were used to identify the microstructure and mineralogical compositions of stabilized soil specimens, respectively while unconfined compression test was used to examine the compressive strength. Test results showed that the addition of recycled bassanite improves the strength of the tested soil. The improvement in the soil strength, based on compressive strength, is in agreement with the SEM and XRD results. The XRD results revealed the presence of various cementation compounds in the soil matrix when recycled bassanite was added. Both the content and ratio of the admixture had a significant effect on the formation of the cementation compounds and the improvement of compressive strength. The formation of ettringite increased with the increase of admixture content in soil mixture for both admixtures used. The ratio of admixture had a clear effect on the reduction of the formation of ettringite in the case of bassanite–cement admixture while it had no significant effect in the case of bassanite–lime admixture. Curing time had a significant effect on the formation of ettringite and the improvement of compressive strength. These results support the suitability of using recycled bassanite produced from gypsum wastes as a low cost and efficient stabilizer material in ground improvement projects.

Utilization of neutralized spent sulfuric acid pickle liquor from metal treatment in cement production

The research addresses the issue of utilization of neutralized spent sulfuric acid pickling liquor, deposited in 1.62 ha lagoons, derived from steel industry, in cement production. Physical–chemical characteristics of the investigated waste revealed low levels of contaminants with the exception of sulfate anions. However, the presence of CaSO4·2H2O revealed a new utilization option for the investigated waste. A key part of the research involved studying the usability of stored waste as a substitute of natural gypsum, acting as a set retarder in cement production. Cement was prepared by grinding Portland clinker with the addition of waste gypsum and then was subjected to the examinations of initial setting time, specific surface, water demand and compressive strength. The analysis of mechanical and physical properties revealed that the tested cement with the addition of waste meets standard requirements for Portland cement. Furthermore, the study of natural radioactivity of the waste did not reveal a rise in the level of radionuclides, thus confirming that the investigated waste can be used for the production of construction materials used in buildings intended for human residence. Utilization of the deposited wastes can help eliminate the environmental hazards regarding sulfuric acid pickle liquor waste and can also provide a low-cost resource of waste gypsum, which can be widely used in the production of construction materials.