Properties and microstructure of lightweight aggregate produced from lignite coal fly ash and recycled glass

The effect of glass addition on the processing, physical properties and microstructure of lightweight aggregate made from lignite coal fly ash from the Megalopolis power station in Greece has been investigated. Fly ash/glass mixes have been rapidly sintered at temperatures between 1040 and 1120 °C in a rotary furnace, and the density, water absorption and pellet strength determined. Sintering 60:40 fly ash:waste glass mixes at 1120 °C produced lightweight aggregate with a mean density of 1.35 g/cm3, water absorption of ∼16% and crushing strength of 7.3 MPa. Major crystalline phases in sintered materials were quartz (SiO2), albite (NaAlSi3O8), moissanite (SiC), hematite (Fe2O3), wollastonite (CaSiO3) and diopside (CaMg(Si2O6)). The work indicates that Megalopolis fly ash combined with waste glass can be used to manufacture lightweight aggregate with properties comparable to commercially available products. Fly ash and glass are potential resources that are currently waste materials in Greece. The processing involving pelletising and sintering in a rotary kiln is similar to that required for other commercially available lightweight aggregates manufactured from shales, clays and slate, and therefore processing costs are expected to be similar. However, avoiding the costs and environmental impacts associated with importing lightweight aggregate or using pumice makes the production of FA/glass lightweight aggregate a viable option

Use of Oil Drill Cuttings as an Alternative Raw Material in Sandcrete Blocks

This research has investigated the use of waste oil drill cuttings treated by thermal desorption in sandcrete, a major construction material used throughout Nigeria and much of West Africa. Sandcrete samples were prepared using a sand to cement ratio of 6:1. The results show that replacing up to 50 wt% of sand by treated oil drill cuttings produced sandcrete with reduced water absorption and reduced sorptivity, increased density and reduced thermal conductivity. In addition, the compressive strengths of samples containing oil drill cuttings were comparable to control samples. The work demonstrates the potential for the beneficial reuse of waste oil drill cuttings treated by thermal desorption in the production of sandcrete blocks with improved properties

19th century London dust-yards: A case study in closed-loop resource efficiency

The material recovery methods used by dust-yards in early 19th century London, England and the conditions that led to their development, success and decline are reported. The overall system developed in response to the market value of constituents of municipal waste, and particularly the high coal ash content of household ‘dust’. The emergence of lucrative markets for ‘soil’ and ‘breeze’ products encouraged dust-contractors to recover effectively 100% of the residual wastes remaining after readily saleable items and materials had been removed by the thriving informal sector. Contracting dust collection to the private sector allowed parishes to keep the streets relatively clean, without the need to develop institutional capacity, and for a period this also generated useful income. The dust-yard system is, therefore, an early example of organised, municipal-wide solid waste management, and also of public–private sector participation. The dust-yard system had been working successfully for more than 50 years before the Public Health Acts of 1848 and 1875, and was thus important in facilitating a relatively smooth transition to an institutionalised, municipally-run solid waste management system in England. The dust-yards can be seen as early precursors of modern materials recycling facilities (MRFs) and mechanical–biological treatment (MBT) plants; however, it must be emphasised that dust-yards operated without any of the environmental and occupational health considerations that are indispensable today. In addition, there are analogies between dust-yards and informal sector recycling systems currently operating in many developing countries

Use of extraction chromatography in the recycling of critical metals from thin film Leach solutions

Phosphors and optoelectronic thin film electronic device layers contain critical metals including lanthanides and indium that should be recycled. Solvent impregnated resins (SIRs) containing (i) DEHPA (ii) DODGAA and (iii) DODGAA with the ionic liquid [C4mim][Tf2N] are investigated in extraction chromatography methodologies to recover and separate critical metals from dilute solutions that model those leached from thin films. Optimum adsorption of metals occurs at pH 1.5-3.5 but is highest on DODGAA-[C4mim][Tf2N]. The recovery and separation of adsorbed metal species on the DODGAA-[C4mim][Tf2N] SIR resin from solutions containing the glass matrix ions, Ca(II) and Al(III), along with In(III) and Sn(IV) or lanthanide ions is achieved by elution with HNO3. Ca(II) and Al(III) are completely eluted with 0.1M HNO3 retaining the target critical metal species on the resin. Separation of In from Sn is achieved by elution of In(III) with 2.5M HNO3 and Sn(IV) with 5M acid. La is separated from the other lanthanides by elution of La(III) with 2.5M HNO3 and the remaining lanthanides with 5M acid. The SIR resins can be reused over a series of at least five cycles of loading, stripping, and rinsing to reduce reagent costs and achieve economic critical metal recovery by extraction chromatography

CLOGGING POTENTIAL OF PERMEABLE CONCRETE

Permeable concrete is used to reduce local flooding in urban areas. However, it is prone to clogging by particulate matter and requires regular maintenance. This paper reports on the performance of permeable concrete exposed to different clogging test methods to further understand this complex phenomena. New methods were developed to study the clogging effect and to define a clogging potential. The tests involve applying flowing water containing sand and/or clay in cycles through the sample and measuring the change in flow rate. Clogging depends on the applied solution and exposure method used. Significant permeability reductions were observed in all samples, particularly when simultaneously exposed to sand and clay. This is because flocculated clay adhered to surface of sand particles and this caused increased clogging

Encapsulation of Cs/Sr contaminated clinoptilolite in geopolymers produced from metakaolin

The encapsulation of caesium (Cs) and strontium (Sr) contaminated clinoptilolite in Na and K based metakaolin geopolymers is reported. When Cs or Sr loaded clinoptilolite is mixed with a metakaolin geopolymer paste, the high pH of the activating solution and the high concentration of ions in solution cause ion exchange reactions and dissolution of clinoptilolite with release of Cs and Sr into the geopolymer matrix. The leaching of Cs and Sr from metakaolin-based geopolymer has therefore been investigated. It was found that Na-based geopolymers reduce leaching of Cs compared to K-based geopolymers and the results are in agreement with the hard and soft acids and bases (HSAB) theory. Cs ions are weak Lewis acids and aluminates are a weak Lewis base. During the formation of the geopolymer matrix Cs ions are preferentially bound to aluminate phases and replace Na in the geopolymer structure. Sr uptake by Na-geopolymers is limited to 0.4 mol Sr per mole of Al and any additional Sr is immobilised by the high pH which causes precipitation of Sr as low solubility hydroxide and carbonate phases. There was no evidence of any other phases being formed when Sr or Cs are added to metakaolin geopolymers