Sampling waste printed circuit boards: Achieving the right combination between particle size and sample mass to measure metal content.

The current worldwide expansion of waste PCB (WPCB) deposits represents both a pressing environmental issue and an economic opportunity, fostering the development of numerous recycling processes across the world. An important input for designing such processes is the metallic content of WPCBs, which is assayed by grinding and leaching samples taken from the stack of WPCBs to be recycled. The content values come with substantial uncertainties, arising mainly from the uneven distribution of the metals within the structure of WPCBs. This study aims to quantify the effects on these uncertainties of the particle size, the mass of the sample digested and the number of digestion replicates. It focused on the abundance of six metals in WPCBs: Cu, Fe, Zn, Pb and Ni, and also Co, which is a critical element for the EU. A batch of 485 kg of WPCBs was put through several shredding and splitting steps to produce three fractions: one shredded to 2 mm, and two ground to 750 µm and 200 µm. From each sample, 16 samples of 0.5 g, 2 g or 5 g were digested in hot aqua regia. Bootstrapping of the results allowed the error around the mean content to be estimated, for each metal and for all the experimental conditions. Considering the largest sample masses and three replicated digestions, the uncertainties for Zn (resp. Ni) were reduced from 35% to 10% (resp. from 70% to 10%) when the particle size was reduced from 2 mm to 200 µm.

Transfer and degradation of polyacrylamide-based flocculants in hydrosystems: a review.

The aim of this review was to summarize information and scientific data from the literature dedicated to the fate of polyacrylamide (PAM)-based flocculants in hydrosystems. Flocculants, usually composed of PAMs, are widely used in several industrial fields, particularly in minerals extraction, to enhance solid/liquid separation in water containing suspended matter. These polymers can contain residual monomer of acrylamide (AMD), which is known to be a toxic compound. This review focuses on the mechanisms of transfer and degradation, which can affect both PAM and residual AMD, with a special attention given to the potential release of AMD during PAM degradation. Due to the ability of PAM to adsorb onto mineral particles, its transport in surface water, groundwater, and soils is rather limited and restricted to specific conditions. PAM can also be a subject of biodegradation, photodegradation, and mechanical degradation, but most of the studies report slow degradation rates without AMD release. On the contrary, the adsorption of AMD onto particles is very low, which could favor its transfer in surface waters and groundwater. However, AMD transfer is likely to be limited by quick microbial degradation.

Innovative process routes for a high-quality concrete recycling.

This study presents alternative methods for the processing of concrete waste. The mechanical stresses needed for the embrittlement of the mortar matrix and further selective crushing of concrete were generated by either electric impulses or microwaves heating. Tests were carried out on lab-made concrete samples representative of concrete waste from concrete mixer trucks and on concrete waste collected on a French demolition site. The results obtained so far show that both techniques can be used to weaken concrete samples and to enhance aggregate selective liberation (that is the production of cement paste-free aggregates) during crushing and grinding. Electric pulses treatment seems to appear more efficient, more robust and less energy consuming (1-3 kWh t(-1)) than microwave treatment (10-40 kWh t(-1)) but it can only be applied on samples in water leading to a major drawback for recycling aggregates or cement paste in the cement production process.

Health promotion in general practice: the views of staff.

Since July 1993 general practices have been offered the responsibility for health promotion programmes to reduce coronary heart disease and strokes. This paper reports on a study which examined the views of GPs and practice nurses on the new arrangements for health promotion. It concludes that there has been an increase in paperwork as result of the changes. It also suggests that practices may have been over-ambitious in the level of health promotion they were trying to provide.