Recovery of metals and other beneficial products from coal fly ash： a sustainable approach for fly ash management

Increasing production and disposal of coal fly ash （CFA） is a matter of serious environment concern. However, CFA contains various beneficial metals and mineral matters whose demand is increasing in the industrialized world, while natural supplies are diminishing. Therefore, recovery of these potential resources from CFA can be an alternative way to save mineral resources, as well as to reduce the environmental burden of CFA disposal. There are numerous methods developed for the recovery of beneficial products from CFA. Based on the US patents and journal literatures, the present review describes the recovery status and technologies of major elements such as Al, Si, Fe and Ti, and trace elements such as V, Ga, Ge, Se, Li, Mo, U, Au, Ag, Pt groups and rare earth elements （REEs） and other beneficial products such as magnetic materials, cenospheres, and unburned carbon from CFA. It also highlights the recovery efficiency and drawbacks for their extraction, and suggests future research to develop satisfactory results in terms of selective recovery and purification.

The effect of abiotic stresses on plant C:N:P homeostasis and their mitigation by silicon

In crop plants, various environmental stresses affect the balance of carbon, nitrogen, and phosphorus(C:N:P), leading to biochemical and physiological alterations and reductions in yield. Silicon(Si) is a beneficial element that alleviates plant stress. Most studies involving silicon have focused on physiological responses, such as improvements in photosynthetic processes, water use efficiency, and antioxidant defense systems. But recent research suggests that stressed plants facing either limited or excessive resources(water, light, nutrients, and toxic elements), strategically employ Si to maintain C:N:P homeostasis, thereby minimizing biomass losses. Understanding the role of Si in mitigating the impact of abiotic stresses on plants by regulating C:N:P homeostasis holds great potential for advancing sustainable agricultural practices in crop production. This review presents recent advances in characterizing the influence of environmental stresses on C:N:P homeostasis, as well as the role of Si in preserving C:N:P equilibrium and attenuating biological damage associated with abiotic stress. It underscores the beneficial effects of Si in sustaining C:N:P homeostasis and increasing yield via improved nutritional efficiency and stress mitigation.

Use of Silicon in Mitigating Ammonium Toxicity in Maize Plants

Silicon is a beneficial element that can mitigate abiotic stresses, such as ammonium toxicity. The objective herein was to evaluate the effects of silicon (Si) on mitigating toxicity caused by excess ammonium in maize plants grown in nutrient solution. An experiment was conducted with maize plants (cultivar DKB 390 VT Pro II) grown in a greenhouse in pots (8 L) in a hydroponic system. The treatments were arranged in a 2 × 2 factorial, consisting of two ammonium concentrations (30 and 60 mmol·L-1) in the absence and presence of Si (10 mmol·L-1), arranged in a completely randomized design with six repetitions. At 28 days after applying the treatments the dry mass of shoots and roots was evaluated, along with accumulation of silicon and nitrogen in the shoots. The use of silicon resulted in increases in the studied variables, regardless of ammonium concentrations. Silicon reduced the effect of toxicity caused by ammonium excess in maize plants, resulting in greater growth and dry matter accumulation.