Phosphorus removal by steel slag from tile drainage water: Lab and field evaluations

Research on the Properties of Steel Slag with Different Preparation Processes

To promote the resource utilization of steel slag and improve the production process of steel slag in steelmaking plants, this research studied the characteristics of three different processed steel slags from four steelmaking plants. The physical and mechanical characteristics and volume stability of steel slags were analyzed through density, water absorption, and expansion tests. The main mineral phases, morphological characteristics, and thermal stability of the original steel slag and the steel slag after the expansion test are analyzed with X-ray diffractometer (XRD), scanning electron microscope (SEM), and thermogravimetric analysis (TG) tests. The results show that the composition of steel slag produced by different processes is similar. The main active substances of other processed steel slags are dicalcium silicate (C2S), tricalcium silicate (C3S), CaO, and MgO. After the expansion test, the main chemical products of steel slag are CaCO3, MgCO3, and calcium silicate hydrate (C-S-H). Noticeable mineral crystals appeared on the surface of the steel slag after the expansion test, presenting tetrahedral or cigar-like protrusions. The drum slag had the highest density and water stability. The drum slag had the lowest porosity and the densest microstructure surface, compared with steel slags that other methods produce. The thermal stability of steel slag treated by the hot splashing method was relatively higher than that of steel slag treated by the other two methods.

Utilizing different types of biomass materials to modify steel slag for the preparation of composite materials used in the adsorption and solidification of Pb in solutions and soil

This study utilized discarded steel slag (SS) as raw material and prepared modified steel slag materials (SS-SBC, SS-NBC, SS-BHA) through modification with biomass materials such as straw biochar (SBC), nutshell biochar (NBC), and biochemical humic acid (BHA). These materials were then applied for the removal of Pb from both solution and soil. The physical and chemical properties of the materials were analyzed using characterization techniques such as SEM, EDS, XRD, and BET. The specific surface area of the modified materials increased from the original 3.8584 m2/g to 34.7133 m2/g, 181.7329 m2/g, and 7.7384 m2/g, respectively. The study then explored the influence of different adsorption conditions on the adsorption capacity of Pb in solution, determining the optimal conditions as follows: initial concentration of 200 mg/L, adsorbent mass of 0.04 g, temperature of 15 °C, and pH = 2. To further investigate the adsorption process, kinetic and isotherm models were established. The results indicated that the adsorption process for all three materials followed a pseudo-second-order kinetic model and Freundlich isotherm model, suggesting a multi-layer chemical adsorption. Thermodynamic analysis revealed that the adsorption process was an exothermic spontaneous reaction. Soil cultivation experiments were conducted to explore the effects of different material addition amounts and cultivation times on the passivation of Pb-polluted soil. Analysis of heavy metal forms in the soil revealed that the addition of modified materials reduced the acid-extractable form of Pb in the soil and increased the residual form, which is beneficial for reducing the migration of Pb in the soil. FT-IR and XPS analyses were employed to study the functional groups, element composition, and valence states before and after adsorption passivation of Pb by the three materials. The results confirmed that the adsorption mechanisms of SS-SBC, SS-NBC, and SS-BHA mainly involved electrostatic adsorption, ion and ligand exchange, and surface precipitation. This study not only provides a new material for adsorbing and immobilizing heavy metals in soil and water but also offers a new approach for the resource utilization of steel slag waste.

Analysis of reactive phosphorus treatment by filter materials at the edge of tile-drained agricultural catchments: A global view of the current status and challenges

Phosphorus losses from agriculture have long generated concern due to the ecological impact on surface waters. Here tile-drained agricultural catchments are a critical source for concentrating and transporting phosphorus bioavailable forms or dissolved reactive phosphorus (DRP). Hence, edge-of-field technologies have been introduced to reduce DRP loads. Filter systems have received special attention due to their targeted approach using a permeable filter material (FM) rich in DRP sorbents. This review explores the performance and applicability of FMs in the aforementioned context because of the growing number of studies. An overall analysis revealed that sorption is preferable to precipitation for DRP retention at the edge-of-field, and that FM pH and particle size affect sorption properties and subsequently DRP retention and lifetime. Thus, FMs with predominant amounts of iron and/or aluminium can be recommended. Such materials generally have an appreciable availability of DRP binding sites, strong bonds with DRP and short reaction times, as well as low desorption, which lead to good operation. On the other hand, FMs with predominant amounts of calcium and/or magnesium are restricted to catchments with favourable conditions unless they have optimal reactivity for DRP. The review also found that hydraulic retention time plays a key role in the performance and applicability of FMs, especially in those dependent on precipitation reactions. Therefore, it is crucial that FMs are designed, constructed and managed according to the catchment conditions-including normally varying flow rates and DRP concentrations-in order to ensure successful operation. This reflects in long-term, high and steady net DRP retention along with low costs, thus improving the FM cost-effectiveness, besides discharging non-harmful effluents to aquatic ecosystems.