Circular Economy and industrial leadership

The relationship between the properties of geopolymers and the characteristics of metakaolin samples used in their preparation has been investigated. Three commercial metakaolin samples have been characterised using 27 Al-NMR to determine the coordination number of Al (IV, V and VI), and by acid and alkali dissolution to determine the reactive Si and Al content. The setting and mechanical properties of geopolymers formed from the metakaolin samples under identical conditions are reported, using Weibull statistics to analyse strength data. Although the metakaolin samples contained different levels of five coordinated aluminium (Al (V)) the mechanical properties of the geopolymers formed were very similar. The reactive fraction of metakaolinite determined by dissolution in 8M NaOH provides the most relevant long-term indicator of geopolymer performance.

The resistance of very high volume fly ash cement pastes and mortars activa ted by Na 2 SO 4 has been monitored following immersion for up to 90 d in 0.1 M HCl, 4.4% Na 2 SO 4 and ASTM-compliant sea water. Changes in the compressive strengths of mortars and in crystalline phases, bond environments, and the microstructure of pastes following immersion were monitored. Experiments were repeated with a comme rcially available sulfate resistant cement. Both cements were found to present adequate resistance to both sea water and the Na 2 SO 4 solution. However, both were severely degraded by acid immersion. Differen ces in potential degradation mechanisms based on the chemistry of the fly ash binder and the reference cement are discussed.

Assessment of the pozzolanic activity of cement replacement materials is increasingly important because of the need for more sustainable cementitious products. The pozzolanic activity of metakaolin, silica fume, coal fly ash, incinerated sewage sludge ash and sand have been compared using the Frattini test, the saturated lime test and the strength activity index test. There was significant correlation between the strength activity index test and the Frattini test results, but the test results from these tests did not correlate with the saturated lime test results. The weight ratio of Ca(OH) 2 to test pozzolan is an important parameter. In the Frattini test and strength activity index test the ratio is approximately 1: 1, whereas in the saturated lime test the ratio is 0.15: 1. This explains why the saturated lime test shows higher removal of Ca(OH) 2 and why the results from this test do not correlate with the other test methods.

The physical and chemical changes taking place in a very high volume fly ash cement paste (FAN-4) following exposure to temperatures up to 1000°C are presented. Tests were repeated with commercially available CEM II/A-M Portland composite-cement (MS). FAN-4 pastes showed impressive residual strengths after heat exposure which increased dramatically when heated previously at 800 or 1000°C. This was in stark contrast to the MS paste, which showed a continual decrease in residual strength following heating and subsequent cooling. The increase in residual strength with FAN-4 paste coincided with a major shrinkage event, which was associated with sintering and the formation of the new mineral phases anorthite, gehlenite, wollastonite, diopside and albite. The MS cement formed generally nonhydraulic calcium silicate phases upon heating at P800°C. The differences in phase formation were linked to different starting elemental compositions. The FAN-4 paste was considerably richer in Si, Al, Fe and alkalis but poorer in Ca. The elemental composition of the binder phase will be an important factor to take into account when determining the high-temperature performance of future cements and concretes, which are likely to contain significantly higher contents of supplementary cementitious materials than is presently the case.

Ambient temperature drying shrinkage in metakaolin-based geopolymer pastes exposed to low relative humidity environments has been investigated. The effect of varying the geopolymer composition (water content, Si:Al ratio, Na:Al ratio and Na + vs K + cations) on the sensitivity to ambient temperature drying shrinkage is reported. The definition of "structural" water as being the minimum water content required to prevent contractions in the gel structure, and thus drying shrinkage from occurring, is introduced. From the results presented, it is clear that the ionic charge density of cations, the total quantity of cations and the relative quantities and stabilities of cation: AlO 4 pairs in the paste are the major factors affecting the sensitivity of pastes to ambient temperature drying shrinkage.

The early age ambient temperature hydration of a hybrid cement formulation containing very high volumes of coal fly ash (~80% by dry mass) and activated by Na 2 SO 4 is presented. The Na 2 SO 4 salt acts as a safe and convenient in situ source of alkali to activate fly ash glassy phases without undesirable effects on cement clinker hydration. Comparison to a reference paste with gypsum instead of sodium sulfate revealed that Na 2 SO 4 reduced setting times, shortened the induction period, and increased early alite hydration and compressive strength development, but also restricted ettringite formation. When replacing the active fly ash component for milled sand of a similar particle size, the Na 2 SO 4-activated pastes set even quicker, no ettringite was observed, and early strengths were considerably reduced. Possible reaction mechanisms in the hybrid pastes are discussed.

The recovery of phosphorus from sewage sludge ash samples obtained from 7 operating sludge incinerators in the UK using a sulfuric acid washing procedure to produce a technical grade phosphoric acid product has been investigated. The influences of reaction time, sulfuric acid concentration, liquid to solid ratio and source of ISSA on P recovery have been examined. The optimised conditions were the minimum stoichiometric acid requirement, a reaction time of 120 minutes and a liquid to solid ratio of 20. Under these conditions, average recoveries of between 72 and 91% of total phosphorus were obtained. Product filtrate was purified by passing through a cation exchange column, concentrated to 80% H 3 PO 4 and compared with technical grade H 3 PO 4 specifications. The economics of phosphate recovery by this method are briefly discussed.

The drivers for increasing incineration of sewage sludge and the characteristics of the resulting incinerated sewage sludge ash (ISSA) are reviewed. It is estimated that approximately 1.7 million tonnes of ISSA are produced annually worldwide and is likely to increase in the future. Although most ISSA is currently landfilled, various options have been investigated that allow recycling and beneficial resource recovery. These include the use of ISSA as a substitute for clay in sintered bricks, tiles and pavers, and as a raw material for the manufacture of lightweight aggregate. ISSA has also been used to form high density glass-ceramics. Significant research has investigated the potential use of ISSA in blended cements for use in mortars and concrete, and as a raw material for the production of Portland cement. However, all these applications represent a loss of the valuable phosphate content in ISSA, which is typically comparable to that of a low grade phosphate ore. ISSA has significant potential to be used as a secondary source of phosphate for the production of fertilisers and phosphoric acid. Resource efficient approaches to recycling will increasingly require phosphate recovery from ISSA, with the remaining residual fraction also considered a useful material, and therefore further research is required in this area.

Hybrid alkaline cements are obtained by alkali-activating cementitious blends in the Na 2 O-CaO-SiO 2-Al 2 O 3-H 2 O system. The present paper discusses the results of activating different cementitious blends containing a low OPC clinker content (<30%) and a high content of supplementary cementitious materials (such as Fly ash). To obtain useful early mechanical strengths (> 15MPa a 2 days) different alkaline activators were used (liquid and solid). The reaction products obtained were also characterised by XRD, SEM/EDX and 27 Al and 29 Si NMR-MAS. The results showed that the main reaction product was a mix of cementitious gels C-AS -H and (N,C)-AS -H, and that their relative proportions were strongly influenced by the calcium content in the initial binder

A hazardous waste assessment has been completed on ash samples obtained from seven sewage sludge incinerators operating in the UK, using the methods recommended in the EU Hazardous Waste Directive. Using these methods, the assumed speciation of zinc (Zn) ultimately determines if the samples are hazardous due to ecotoxicity hazard. Leaching test results showed that two of the seven sewage sludge ash samples would require disposal in a hazardous waste landfill because they exceed EU landfill waste acceptance criteria for stabilised non-reactive hazardous waste cells for soluble selenium (Se). Because Zn cannot be proven to exist predominantly as a phosphate or oxide in the ashes, it is recommended they be considered as non-hazardous waste. However leaching test results demonstrate that these ashes cannot be considered as inert waste, and this has significant implications for the management, disposal and re-use of sewage sludge ash.

Blended cements that contain a high content of fly ash and a low content of Portland cement typically suffer from low early strength development and long setting times. Recently, one method of overcoming these problems has been to use an alkali activator to enhance the reactivity of fly ash particles at early ages. Such cements can be grouped under the generic term "hybrid alkaline cements", where both cement clinker and fly ash, encouraged by the presence of alkalis, are expected to contribute to cementitious gel formation. The work presented here examines some of the durability aspects of high fly ash content hybrid alkaline cement. Specifically, the aspects investigated were: exposure at high temperatures (up to 1000°C), resistance to immersion in aggressive solutions and susceptibility to the alkali aggregate reaction. All tests were repeated with a commercially available sulfate resistant Portland cement for comparison. When exposed to high temperatures, the hybrid alkaline cement showed strikingly different behaviour compared to the control Portland cement, showing fewer micro-cracks and maintaining residual compressive strengths at least equal to original strengths. Beyond 700°C, the hybrid alkaline cement began to sinter, which resulted in shrinkage of around 5% and a 100% increase in residual compressive strengths. No such sintering event was noted in the control Portland cement, which showed a drastic loss in residual compressive strengths upon heating. In immersion tests, the hybrid alkaline cement possessed excellent resistance to sulfate and seawater attack, similar to the control sulfate resistant cement. Both cements were however severely degraded by immersion in 0.1M HCl for 90 days. Both binders complied with the accelerated alkali-aggregate test but when this test was extended, the hybrid alkaline binder showed much greater dimensional stability. Possible reasons for the differences in durability behaviour in both cements are discussed, based on experimental evidence provided.

In hybrid alkaline fly ash cements, a new generation of binders, hydration, is characterized by features found in both ordinary portland cement (OPC) hydration and the alkali activation of fly ash (AAFA). Hybrid alkaline fly ash cements typically have a high fly ash (70 wt % to 80 wt %) and low clinker (20 wt % to 30 wt %) content. The clinker component favors curing at ambient temperature. A hydration mechanism is proposed based on the authors' research on these hybrid binders over the last five years. The mechanisms for OPC hydration and FA alkaline activation are summarized by way of reference. In hybrid systems, fly ash activity is visible at very early ages, when two types of gel are formed: C-S-H from the OPC and N-AS -H from the fly ash. In their mutual presence, these gels tend to evolve, respectively, into C-AS -H and (N,C)-AS -H. The use of activators with different degrees of alkalinity has a direct impact on reaction kinetics but does not modify the main final products, a mixture of C-AS -H and (N,C)-AS -H gels. The proportion of each gel in the mix does, however, depend on the alkalinity generated in the medium.

The potential of six different extractants to recover phosphorus (P) from incinerated sewage sludge ash (ISSA) was evaluated. Secondary effects such as the co-dissolution of Zn and Cu were also considered. The residual ISSA from each study was assessed in particular detail, focusing on the leachability of remaining Zn and Cu, major element composition, crystalline phases and overall degree of crystallinity and particle size distribution. The residual ISSA was also evaluated as a pozzolanic material using a Strength Activity Index (SAI) test with mortars containing Portland cement with a 20% substitution by ISSA. All results were compared to tests with untreated ISSA. Overall, the use of 3 of the 6 extractants could be ruled out due to poor P recovery potential and/or a serious compromise of the potential reuse of residual ISSA in Portland cement-based materials. The results highlight the added value of considering the potential reuse of residual ISSA when trying to optimize P recove...

Chemical extraction of phosphorus (P) from incinerated sewage sludge ash (ISSA) is adversely influenced by co-dissolution of metals and metalloids. This study investigated P recovery and leaching of Zn, Cu, Pb, As and Ni from ISSA using inorganic acids (sulphuric acid and nitric acid), organic acids (oxalic acid and citric acid), and chelating agents (ethylenediaminetetraacetic acid (EDTA) and ethylene diamine tetramethylene phosphonate (EDTMP)). The aim of this study was to optimize a leaching process to recover P-leachate with high purity for P fertilizer production. The results show that both organic and inorganic acids extract P-containing phases but organic acids leach more trace elements, particularly Cu, Zn, Pb and As. Sulphuric acid was the most efficient for P recovery and achieved 94% of total extraction under the optimal conditions, which were 2-h reaction with 0.2 mol/L HSO at a liquid-to-solid ratio of 20:1. EDTA extracted only 20% of the available P, but the leachates ...

The recovery of phosphorus (P) from acid extracts of incinerated sewage sludge ash (ISSA) is invariably complicated by the co-dissolution of metal(loid)s. An extra purification treatment step is thus needed, which reduces the efficiency of P recovery. This study developed a two-step extraction method which can produce highly purified P-extract where ISSA is treated first with ethylenediaminetetraacetatic acid (EDTA) and then with sulphuric acid. The recovery conditions of this two-step extraction method were optimized (pre-extraction by 0.02 mol/L of EDTA at a liquid to solid ratio (L/Kg) of 20:1 during 120 min, then extraction by 0.2 mol/L sulphuric and at a liquid to solid ratio of 20:1 during 120 min). Compared with direct extraction by sulphuric acid (namely, single-step leaching), the two-step extraction method dissolved 2.34 mmol/kg ISSA less of P, but with 5.16 mmol/kg ISSA less of *Revised Manuscript (clean for typesetting) Click here to view linked References 2 metal(loid) contamination. Furthermore, the potential for co-precipitation of P and the metal(loid) contaminates in the extracts (both single-step extraction and the two-step extraction methods) was examined from pH 2 to 12 (adjusted by addition of NaOH and Ca(OH) 2). By applying Ca(OH) 2 and at the optimal pH of 4, the two-step extraction method could significantly increase CaP in the precipitate and notably decreased the metal(loid) contaminants by 50% compared to the single-step method.

Purpose One possible reason for the poor uptake of the EU Ecolabel for furniture products may be that the criteria are too complex for applicants. Consequently, it was decided to develop a method which quantifies criteria complexity and subsequently, to propose ways for its reduction, which could be considered in future criteria revision. Methods The requirements behind the voluntary EU Ecolabel criteria for furniture products set out in Commission Decision (EU) 2016/1332 have been scored with a “criteria complexity index” (CCI), based on the answers to a series of six questions that relate to the effort required for proper assessment and verification. The criteria, and associated CCI values, have been grouped on a per material basis, allowing a “material complexity index” (MCI) to be calculated and consequently, a “furniture complexity index” (FCI) has been calculated as a function of the materials in different furniture products. Results and discussion Overall, it was found that C...

Purpose Material efficiency encompasses a range of strategies that support a reduction of material consumption and waste production from a product's life cycle perspective and which can help the transition towards a circular economy. The aim of this paper is to analyse the state of implementation of material efficiency requirements for products as set out in existing EU Ecolabel criteria, consider possible improvements, identify current limitations and describe potential or existing synergies with other EU policies and initiatives. Methods Key concepts related to material efficiency have been provided and classified into three groups which are, in order of decreasing priority: reduction, reuse, and recycling/recovery. This classification system has then been used for the analysis of existing requirements set out for different EU Ecolabel products. This includes a description of potential environmental benefits, trade-offs, market barriers and risks. Material efficiency concepts have then been cross-checked with other EU policies and initiatives. Results and discussion Looking at EU Ecolabel criteria for 26 different product groups revealed a broad range of material efficiency aspects, some of which are influenced by the nature of the product group itself. Some material efficiency aspects were broadly integrated into EU Ecolabel criteria through complementary strategies (e.g. design for durability, recyclability, availability of spare parts, reversible disassembly and provision of information). However, ways to implement additional material efficiency requirements (e.g. minimum lifetime of products) should be sought further. A symbiotic relationship can exist between the EU Ecolabel and many policy tools in the sense that regulatory and standardisation frameworks can offer a robust basis for justifying the integration of material efficiency aspects in the EU Ecolabel, while the EU Ecolabel can explore and promote approaches targeted at front runners in material efficiency aspects in a voluntary manner. Conclusions The experience gained from implementing material efficiency aspects in the EU Ecolabel could serve as a reference for shaping design, communication or policy initiatives aimed at the promotion of a more circular economy. Attempts to quantify the impacts from material efficiency measures should be also integrated systematically in future research, with the support of tools like life cycle assessment. However, additional considerations of political, technical and socioeconomic nature must be considered when assessing the relevance, feasibility and ambition level of any material efficiency-related requirements.