Basic Properties of fly Ash/Slag -Concrete Slurry Waste Geopolymer Activated by Sodium Carbonate and Different Silicon Sources

As a kind of granular waste with complex composition and alkali corrosiveness, concrete slurry waste (CSW) has severe recycling limitations in the ordinary Portland cement (OPC). Considering this, a new type of geopolymer, prepared by granulated blast furnace slag/fly ash, concrete slurry waste, and powdered activators (sodium carbonate and different silicon sources including sodium metasilicate pentahydrate and silica fume), was adopted to conduct a comparative study with the OPC counterpart. In this study, the homogenized CSW was mixed in the OPC and geopolymer with a constant ratio of 50 wt%, respectively. Then the properties were studied in terms of the flowability, setting times, mechanical strengths, and microstructures. The results showed that better flowability (200 mm) could be achieved in the obtained geopolymer than in the OPC reference group (95 mm) by increasing the powdered activators. The setting time of the OPC was significantly shortened due to the addition of CSW. The strengths of geopolymer were supported by the produced C-A-S-H and carbonates, with less chemically bonded water than the hydration products in the reference group. The dominant size of pores in the hardened geopolymer was much smaller than that in the OPC group which was 80 nm. Silica fume could be the alternate of the sodium metasilicate pentahydrate and had an insignificant negative impact on the fresh and hardened properties and microstructures of the geopolymer when the incorporation rate was within 5%.

Design, Synthesis, and Implementation of Sodium Silylsilanolates as Silyl Transfer Reagent

There is an increasing demand for facile delivery of silyl groups onto organic bioactive molecules. One of the common methods of silylation via a transition metal-catalyzed coupling reaction employs hydrosilane, disilane, and silylborane as major silicon sources. However, labile nature of the reagents or harsh reaction conditions sometimes renders them inadequate for the purpose. Thus, a more versatile alternative source of silyl groups has been desired. We hereby report a design, synthesis, and implementation of new storable sodium silylsilanolates that can be used for the silylation of aryl halides and pseudohalides in the presence of a palladium catalyst. The new method allows a late-stage functionalization of polyfunctionalized compounds with a variety of silyl groups. Mechanistic studies indicate that 1) a nucleophilic silanolate attacks a palladium center to afford a silylsilanolate-coordinated arylpalladium intermediate and 2) a polymeric cluster of silanolate species assists in the intramolecular migration of silyl groups, which would pro-mote an efficient transmetalation.<br>

Effect of silicon on reduction the availability of toxic elements in the soil: a brief review

Soil pollution is a major environmental problem and also makes food production impossible, since 95% of food produced worldwide originates in the soil. There are numerous practices that when improperly made can cause soil contamination, in agriculture the inadequate use of fertilizers and agrochemicals can cause soil contamination by toxic elements. Silicon is already present in the soil in a natural way, but in recent years research is being developed using silicon-based residues to increase plants resistance to pests and diseases, such as soil corrective and for increased productivity, the results are satisfactory. Many published studies show the benefits of silicon in reducing plants stress, but there is still little information about silicon as a remediator of toxic elements in the soil, so the objective of this work was to search for already published works on this theme. Studies were found using different silicon sources and the application occurred in soils contaminated mainly with Zn, Cd, Cu and Pb.

Plants sustain the terrestrial silicon cycle during ecosystem retrogression

The biogeochemical silicon cycle influences global primary productivity and carbon cycling, yet changes in silicon sources and cycling during long-term development of terrestrial ecosystems remain poorly understood. Here, we show that terrestrial silicon cycling shifts from pedological to biological control during long-term ecosystem development along 2-million-year soil chronosequences in Western Australia. Silicon availability is determined by pedogenic silicon in young soils and recycling of plant-derived silicon in old soils as pedogenic pools become depleted. Unlike concentrations of major nutrients, which decline markedly in strongly weathered soils, foliar silicon concentrations increase continuously as soils age. Our findings show that the retention of silicon by plants during ecosystem retrogression sustains its terrestrial cycling, suggesting important plant benefits associated with this element in nutrient-poor environments.