Laboratory evaluation of acid leaching conditions to purify gypsum from refurbishment plasterboard waste

This work presents results related to a novel recycling process for gypsum from refurbishment plasterboard waste developed within the European Union’s Horizon 2020 research project ICEBERG. One of the main challenges in recycling gypsum from refurbishment plasterboard waste for the production of new plasterboards comes from the difficulty to achieve consistent chemical purity levels > 92 wt% via current physical treatment technologies. The main objective of this work is to evaluate different acid leaching conditions to maximise the acid leaching process efficiency. The impact of gypsum particle size, gypsum/solution ratio, heating rate, stirring rate and gypsum slurry volume on the chemical purity of recycled gypsum was determined. Gypsum particles sizes µm, slow heating rate of 4 °C/min and stirring rates of 150 rpm produced recycled gypsum with the highest purity. This work has identified for the first time the optimum laboratory-scale acid leaching conditions to produce high purity recycled gypsum from refurbishment plasterboard waste. </p

A methodologic approach based on hydrocyclone separation and acid leaching to purify gypsum from refurbishment plasterboard waste

One of the main challenges in recycling gypsum from refurbishment plasterboard waste for the production of new plasterboards comes from the difficulty to achieve consistent purity values higher than 92 wt% via current treatment technologies. These treatments generally rely solely on magnetic and manual physical separation combined with grinding. Although gypsum purity values ranging from 75 wt% to 90 wt% can be achieved, this depends mainly on the quality of the refurbishment plasterboard waste received, as current treatments have limited efficiency and customisation possibilities. As a result, the highest practical rate of recycled gypsum in new plasterboards is currently around 20 wt%. Therefore, physical and chemical treatments have the potential to increase the content of recycled gypsum in new plasterboards. As part of the ICEBERG project from the European Union's Horizon 2020 Research and Innovation Framework Programme under grant agreement No. 869336, hydrocyclone separation and acid purification have been evaluated in this work to achieve purity values above 96 wt% in gypsum from refurbishment plasterboard waste. The plasterboards were crushed and sieved to obtain gypsum particles less than 250 µm in size. For hydrocyclone separation testing, a centrifugal pump was used to produce a gypsum slurry in a mixing tank and to feed the slurry to a commercial mini-hydrocyclone of 2 inches in diameter. Acid leaching was performed at atmospheric pressure on the initial waste gypsum and on a sample collected at the hydrocyclone, using different temperatures, residence times and sulphuric acid solutions. The purity of gypsum obtained from individual and sequential hydrocyclone separation and acid leaching tests was determined through X-ray fluorescence. Furthermore, the calcination behaviour dihydrate phase content of the sample with the highest purity was determined through thermal gravimetric analysis. Hydrocyclone separation was not effective for gypsum purification but acid leaching at 90 °C for 1 hour using a 5 wt% H2SO4 solution produced recycled gypsum with more than 96 wt% chemical purity and dihydrate content

Impact of circular silica aerogel on plasterboard recycling

Silica aerogels have high specific surface area, high porosity, low density, and high thermal insulation values. These properties enhance the thermal performance of plasterboards but can have deleterious effects on the mechanical properties. At the end of life, plasterboards containing silica aerogel could be recycled via physical and acid leaching purification processes. The main aim of this work was to determine the impact of circular silica aerogel on plasterboard recyclability. Circular silica aerogel was produced through hydrothermal conversion of silica-based building waste. The circular silica aerogel was easily recovered during the acid leaching purification stage of the recycling process. Future work will evaluate the impact of silica aerogel on the thermal conductivity and mechanical strength of plasterboard containing circular silica aerogel.</p

Hyperspectral imaging sorting of refurbishment plasterboard waste

Post-consumer plasterboard waste sorting is carried out manually by operators, which is time-consuming and costly. In this work, a laboratory-scale hyperspectral imaging (HSI) system was evaluated for automatic refurbishment plasterboard waste sorting. The HSI system was trained to differentiate between plasterboard (gypsum core between two lining papers) and contaminants (e.g., wood, plastics, mortar or ceramics). Segregated plasterboard samples were crushed and sieved to obtain gypsum particles of less than 250 microns, which were characterized through X-ray fluorescence to determine their chemical purity levels. Refurbishment plasterboard waste particles 98 wt%. These findings underpin the potential implementation of an industrial-scale HSI system for plasterboard waste sorting.</p

Laboratory scale evaluation of hyperspectral imaging sorting of refurbishment plasterboard waste

At present, post-consumer plasterboard waste sorting is carried out manually by operators, which is time consuming and can be costly. In this work, a hyperspectral imaging system has been evaluated for automatic plasterboard waste sorting. Segregated plasterboard samples were crushed and sieved to obtain gypsum particles less than 250 microns, which were characterised through X-ray fluorescence to determine their chemical purity levels. It was found that the chemical purity of gypsum from refurbishment plasterboard waste obtained with the laboratory scale HSI-based sorting system was close to 96 wt%. Refurbishment plasterboard waste particles < 10 mm in size were not processed with the HSI-based sorting system because the manual processing of these particles at laboratory scale would have been very time-consuming. Since refurbishment plasterboard waste particles < 10 mm in size contained very small amounts of impurities, the segregated gypsum obtained from this unprocessed material had a chemical purity similar to that of the sorted plasterboard. The combination of unprocessed refurbishment plasterboard waste < 10 mm with sorted plasterboard ≥ 10 mm in size would lead to a plasterboard recovery yield above 98 wt%

Templates for qPCR-based BER activity assay.

<p>Whole cell extracts were isolated from brain tissue and exposed to a template DNA containing a single nucleotide lesion (A) and control template (B). BER activity was calculated by comparing the ΔΔCt values (Ct is the number of cycles required for the fluorescent signal to cross the threshold) of the repaired and control templates.</p

OCM impairment is involved in ethanol-induced oxidative DNA damage and neuronal apoptosis effects in the PFC.

<p>The brain sections (PFC) of WT and <i>Mthfr+/−</i> mice exposed for 3 weeks or 4 days (acute) to the Lieber-DeCarli liquid diet with- or without ethanol (5%) were triple-labeled with NeuN (purple), TUNEL (green) and cleaved caspase-3 (red). Hoechst 33342 (blue) was used to identify all cell nuclei. Fluorescence was visualized by confocal microscopy. Scale bar = 20 µm. Note increased number of TUNEL/caspase-3-positive neurons in PFC of <i>Mthfr+/−</i> mice chronically exposed to ethanol, compared with corresponding WT mice (arrows). Also, note a higher density of TUNEL/caspase-3-positive neurons in PFC of chronically, compared with acutely exposed to ethanol WT mice (arrows).</p

PFC is more vulnerable to ethanol-induced neuronal apoptosis than hippocampus.

<p>Brain sections double-labeled with TUNEL and MAP-2 in the PFC and hippocampus (Hip) and quantified by stereological counting; Values are means ± SEM; *p<0.01. Neither the number of MAP-2-positive cells (neurons) nor volumes of the brain structures were affected by chronic 3-week ethanol exposure. Note significantly higher density of TUNEL- positive neurons in PFC than in hippocampus of ethanol-exposed mice.</p

OCM impairment is involved in ethanol impact on DNA repair in the PFC.

<p>(A) Blood Hcy levels in WT and <i>Mthfr+/−</i> mice following acute or chronic 3- week (3 w) or 5-week (5 w) ethanol exposure. Values are means ± SEM; *p<0.01; **p<0.001. Note chronic alcohol-induced increase in blood Hcy levels, compared with the acute exposure and the heightening this increase by MTHFR deficiency. (B) DNA repair activity in the PFC of WT and <i>Mthfr+/−</i> mice exposed to acute and chronic ethanol. Values are means ± SEM; *p<0.01; **p<0.005; ***p<0.002. Note a decrease in DNA repair activity in the PFC following 3-week (3 w) and even more so following 5 week (5 w) exposure, compared with acute alcohol exposure and a significant exaggeration of this decrease by MTHFR deficiency.</p

PFC is more vulnerable to ethanol-induced oxidative stress than hippocampus.

<p>(A) oxo-8dG expression in neurons (neuronal marker MAP-2) was quantified in PFC and hippocampus (Hip) by stereological counting. Neither the number of neurons nor volumes of the brain structures were affected. Values are mean ± SEM; *p<0.01. (B) Oxo-8dG expression in neurons normalized to corresponding controls (Δ). Note significantly higher density of oxo-8dG -labeled neurons and Δ in PFC, compared with hippocampus of ethanol-exposed mice. (C) DNA repair activity in response to oxidative DNA damage (oxo-8dG) assessed by qPCR in whole cell extracts obtained from PFC and hippocampus (Hip) of control mice and mice exposed to acute or chronic ethanol. Values are means ± SEM; *p<0.05, **p<0.01. Note the response to oxidative DNA damage by PFC lysate is significantly stronger than those in the hippocampus.</p