High-quality gypsum binders based on synthetic calcium sulfate dihydrate produced from industrial waste

High-strength gypsum binder with improved water-resistance coefficient derived from industrial wastes

The article presents the possibility of increasing the water resistance of gypsum binders (GBs) obtained based on synthetic gypsum by introducing additives derived from industrial wastes. Regularities were obtained for the influence of the type and amount of additives on the water/gypsum ratio (W/G), strength indicators and water resistance of high-strength GB. The introduction of a single-component additive to improve water resistance does not have a significant effect. Complex additives based on Portland cement, granulated blast-furnace slag, electric steel-smelting slag, expanded clay dust and granite screenings of various fractions have been developed that make the maximum contribution to improving the water resistance of a high-strength GB based on synthetic calcium sulphate dihydrate, which made it possible to increase the water-resistance coefficient from 0.39 to 0.82.

Study on Early Hydration Mechanism of Double-Liquid Grouting Material Modified by Composite Early Strength Agent

To achieve an adjustable setting time and significantly improved early strength of a new type of sulphoaluminate cement-based double-liquid grouting material (SACDL), the effects of calcium formate, sodium sulfate, lithium carbonate, and a composite early strength agent on the setting hardening and early hydration behavior of SACDL paste were studied by means of setting time, fluidity, compressive strength, and viscosity tests. The results showed that the adsorption and osmosis of calcium formate, the complex decomposition of sodium sulfate, the precipitation polarization of lithium carbonate and the synergistic action of the composite early strength agent could accelerate the early hydration rate of SACDL, shorten the coagulation time, and improve the early strength of SACDL. The composite effect of 0.8% calcium formate and 0.5% sodium sulfate is the most significant in promoting coagulation and early strength; the initial setting time and final setting time of the slurry were shortened to 5 min and 10 min, respectively; and the 3 h compressive strength was capable of reaching 16.7 MPa, 31% higher than that of the blank group. In addition, X-ray diffraction and SEM morphology observation were used to study the composition of the hydration products and the evolution of the microstructure, which revealed the early hydration mechanism of SACDL under the synergistic effect of the composite early strength agent: (1) The solubility of tricalcium aluminate (C3A) and dihydrate gypsum (CaSO4·2H2O) increased under the low content composite early strength agent condition, which increased the ettringite (AFt) formation rate. HCOO- was able to penetrate the hydration layers of tricalcium silicate (C3S) and dicalcium silicate (C2S), accelerating the dissolution of C3S and C2S and promoting the early hydration of SACDL. (2) Under the condition of a high dosage of the composite early strength agent, the further increase in Ca2+ concentration promoted the crystallization nodules and precipitation of CH and accelerated the formation of calcium silicate hydrate (C-S-H) gel. C-S-H was filled between a large number of rod-like AFt crystals, thus making the structure more dense.

Approaches for filtrate utilization from synthetic gypsum production

Waste recycling and industrial wastewater treatment have always been of interest. A green approach was developed for the filtrate of synthetic gypsum production from water treatment coagulation sediments and spent sulfuric acid. Due to the high concentration of iron sulfate, concentrated filtrate showed good coagulation results, which were 5% lower than pure iron sulfate. In addition, a high concentration of iron facilitates its use as a precursor for synthesizing magnetic sorbents and photocatalysts. Such materials were synthesized by the solution combustion synthesis method. Oil sorption capacity reached 1.8 g/g, comparable to some synthetic materials and higher than sorption materials based on natural materials. Photodegradation of acid telon blue dye after 90 min of irradiation time was 82.7% with catalyst derived from filtrate compared to the just dye solution with 17.6% efficiency. The reaction rate constant for the photocatalyst sample was up to 11.4-fold higher compared with only UV treatment. The neutralized filtrate containing sulfur, calcium, magnesium, and sodium has been tested as a complex fertilizer. The results of bioindication for oil radish showed up to a 15% increase in the shoot length. A number of techno-economic indicators show that such an approach is advantageous from a technological, environmental, and economic point of view.

Reuse of walnut shell waste in the development of fired ceramic bricks

The development of agricultural waste-doped fired bricks is an important step toward achieving lightweight eco-efficient bricks with improved thermal insulation property. Recent research in masonry has been tailored towards the production of energy-efficient building by incorporating waste materials as additives. This effectuates a safe waste disposal, cost effectiveness, and also serve as a giant stride towards environmental sustainability. This study examines the viability of using walnut shell as additive in fired clay at various firing temperatures. Pulverized walnut shell was added to clay at a proportion of 0-10 wt.% by weight of clay. The samples were fired at temperatures of 950 °C and 1100 °C. The samples were probed for mechanical properties and durability. Morphology of the brick samples were examined under scanning electron microscope. The result of the research showed increased water absorption and specific heat capacity while mechanical and bulk density were observed to reduce. Linear shrinkage and thermal conductivity reduced with increase in walnut content of which linear shrinkage and thermal conductivity values experienced at 1100 °C was higher than at 950 °C. Resistance of bricks to salt crystallization increased with firing temperature. All samples met various standard requirement for masonry except sample prepared with 10 wt.% walnut shell whose compressive and flexural strengths fell below the required standard. The study established the use of walnut shell for development of sustainable energy-efficient bricks.

An integrated strategy for nutrient harvesting from hydrolyzed human urine as high-purity products: Tracking of precipitation transformation and precise regulation

The nutrient recovery from source-separated urine is of great significance for a sustainable and closed nutrient loop. However, common urine-processing techniques have several constraints, including inefficient recovery, low product purity and incapability of simultaneously harvesting multiple nutrients. In this study, an integrated strategy of P precipitation and N stripping was first proposed to harvest nutrients from hydrolyzed human urine as high-purity products via precisely regulating Ca/P dosing ratio. Ca(OH)2 was utilized to trigger Ca-P precipitation and elevate pH level. Different from the previously reported conventional struvite method, P recovery was oriented to calcium phosphate. P harvesting behavior was investigated as a function of key factors including initial P concentration and the dosing ratio. A thermodynamic model was constructed to unveil the precipitation transformation mechanism and visualize P recovery for an enhanced controllability. For N harvesting, Ca(OH)2 was dosed to increase the pH of the urine to converts ammonium to ammonia. The resulting ammonia was stripped and then adsorbed by H2SO4 as high-purity ammonium sulfate. Moreover, the sulfate derived from acidification treatment was recovered as calcium sulfate in the interests of material recycling and mitigating secondary contaminations. Results exhibited P recovery efficiency could reach 100 % and purity for calcium phosphate could be above 90 % within a Ca/P ratio range of 1.67-2.0. Further boosting pH to 12, over 85 % of S and 95 % of N was retrieved. The comprehensive scheme provides an efficient approach towards the precise P and N harvesting from hydrolyzed urine and advances the knowledge of precipitation transformation mechanism.

Mathematical modelling, multi-objective optimization, and compliance reliability of paper-derived eco-composites

The quest for cost-effective and thermal efficient structural materials onto beating the high cost of construction is gaining more attention among researchers. This study focused on the blending of cement and sand with waste paper pulp into cost-effective structural materials. The composites were prepared in four mix groups with each containing a fixed amount of sand at 5, 10, 15, and 20 wt.% (by weight of pulp). Cement was varied at 10, 20, 30, and 40 wt.% in each group, and curing was done for 28 days. Properties evaluated are compressive, bending, and splitting strengths. It was observed that increasing cement and sand contents enhanced strengths; howbeit, the blend of 30 wt.% cement/15 wt.% sand resulted in a reduction in bending strength even as 30 wt.% cement/20 wt.% sand engendered a decrease in bending and splitting strength. The microstructural features showed that inherent fibers of the pulp were well bonded with hydration products and sand content yielding good performance in the composites. The optimization procedure carried out depicted a combination of 35.27% cement and 20% sand as the optimum composition. Experimental outcomes were modelled for the purpose of prediction of responses. The models were confirmed statistically fit showing how varying cement content affected strength responses at fixed sand proportion. ANOVA affirmed the significant contribution of cement and sand on the strength responses. Compliance reliability was observed to be dependent on the interactive pattern between cement and sand. Going by the standard prescription for the strength properties, cement and sand content of 35.27 and sand 20 wt.% satisfied all strength requirements for low-cost construction having a compliance reliability of 1.31.

Recycling of synthetic waste wig fiber in the production of cement-adobe for building envelope: physio-hydric properties

Waste wigs are often disposed off in their volume on landfills, thus constituting a nuisance to the environment. Recycling these wigs in masonry bricks is a way via which they can be recycled and reused. On such premise, waste wig fiber (WWF) was recycled by incorporating into the cement-sand-clay composite mix for masonry bricks production. The challenges masonry bricks face include shrinkage and water susceptibility; hence, the contributory effect of WWF on physio-hydric properties was assessed in this study. Sample preparation entailed blending of cement, sand, clay soil, and waste wig fiber. The control mix was prepared by commixing clay with 10% cement (by clay volume) and 20% sand (by clay volume). Other mix proportions were reinforced with 1, 2, 3, 4, and 5% WWF by clay volume. Prepared composite brick samples were cured for 28 and 56 days and tested for physio-hydric properties. Results revealed WWF contributed significantly in improving hydro-resisting properties by minimizing porosity, water and moisture absorption, capillary suction, and water permeability. Furthermore, WWF contributed to dimensional stability by reducing shrinkages and weight loss. Hydration time impacts significantly in reducing apparent porosity, water permeability coefficient, moisture and water absorption, and capillary suction coefficient and increasing apparent density, weight loss, linear, and volumetric shrinkage. The general outcome depicts that WWF showed promising performance in bricks developed in enhancing water and moisture susceptibility resistance and promoting mass and dimensional stability, hence can be employed in reinforcing cement adobe bricks at an optimum mix of 5% vol fraction.

Synergistic advanced oxidation process for enhanced degradation of organic pollutants in spent sulfuric acid over recoverable apricot shell-derived biochar catalyst

The sulfuric acid-based alkylation process, which leads the industrial application market, still struggles with effectively removing a large number of organic pollutants from hazardous spent sulfuric acid. A synergistic advanced oxidation process was constructed to degrade the organic pollutants with H2O2 and sodium persulfate as the synergistic oxidants and apricot shell-derived biochar (OBC) as the catalyst. Taking the total organic carbon (TOC) and the color scale as the indices, the effects of critical experimental factors, i.e., reaction temperature, initial oxidant concentration, catalyst dosage, and aeration rate, were optimized. The results showed that the removal rates of TOC and the color of the spent sulfuric acid reached ∼91% and 96.6%, respectively, after 150 min under the optimum conditions. Besides, the efficient and low-cost OBC catalyst developed in this study could be continuously used for at least four times with about 75% TOC removal and 80% color removal, exhibiting favorable stability and good resistance to acid corrosion. Further study confirmed that the SO4-˙ and ˙OH radicals generated in the synergistic advanced oxidation process strengthened the degradation and elimination of organic pollutants. The synergistic advanced oxidation process could provide a feasible insight for spent sulfuric acid treatment.