M. Contreras

Fractionation and fluxes of metals and radionuclides during the recycling process of phosphogypsum wastes applied to mineral CO2 sequestration

The industry of phosphoric acid produces a calcium-rich by-product known as phosphogypsum, which is usually stored in large stacks of millions of tons. Up to now, no commercial application has been widely implemented for its reuse because of the significant presence of potentially toxic contaminants. This work confirmed that up to 96% of the calcium of phosphogypsum could be recycled for CO2 mineral sequestration by a simple two-step process: alkaline dissolution and aqueous carbonation, under ambient pressure and temperature. This CO2 sequestration process based on recycling phosphogypsum wastes would help to mitigate greenhouse gasses emissions. Yet this work goes beyond the validation of the sequestration procedure; it tracks the contaminants, such as trace metals or radionuclides, during the recycling process in the phosphogypsum. Thus, most of the contaminants were transferred from raw phosphogypsum to portlandite, obtained by dissolution of the phosphogypsum in soda, and from portlandite to calcite during aqueous carbonation. These findings provide valuable information for managing phosphogypsum wastes and designing potential technological applications of the by-products of this environmentally-friendly proposal.

Valorisation of waste ilmenite mud in the manufacture of sulphur polymer cement

This paper reports the preparation of sulphur polymer cements (SPCs) incorporating waste ilmenite mud for use in concrete construction works. The ilmenite mud raw material and the mud-containing SPCs (IMC-SPCs) were characterised physico-chemically and radiologically. The optimal IMC-SPC mixture had a sulphur/mud ratio (w/w) of 1.05 (mud dose 20 wt%); this cement showed the greatest compressive strength (64 MPa) and the lowest water absorption coefficient (0.4 g cm(-2) at 28 days). Since ilmenite mud is enriched in natural radionuclides, such as radium isotopes (2.0·10(3) Bq kg(-1)(228)Ra and 5.0·10(2) Bq kg(-1)(226)Ra), the IMC-SPCs were subjected to leaching experiments, which showed their environmental impact to be negligible. The activity concentration indices for the different radionuclides in the IMC-SPCs containing 10% and 20% ilmenite mud met the demands of international standards for materials used in the construction of non-residential buildings.

Manufacture of Ceramic Bodies by Using a Mud Waste from the TiO2 Pigment Industry

The main objective of this paper is focused in the use of waste generated by the TiO2 pigment industry, ilmenite mud (MUD), on the production of ceramic bodies. These ceramic bodies were produced from mixtures of a commercial red stoneware mixture (RSM) with different concentrations of mud (3, 5, 7, 10, 30 and 50 wt%). The samples were sintered to simulate a fast-firing process. The sintering behaviour of the fired samples was evaluated according to ISO rules by linear shrinkage, water absorption and porosity measurements. Both green powder and fired samples were characterised by means of X-ray diffraction (XRD), differential scanning calorimetry (DSC/TG), field emission scanning electron microscopy (FESEM) and bending strength measurements. Moreover, the activity concentrations of radionuclides were measured by high-resolution low-background gamma spectrometry, because this mud is a NORM (Naturally Occurring Radioactive Material) waste. Finally, the TCLP leaching test (Toxicity Characteristic Leaching Procedure, USEPA) was performed to assess the risks of use tiles from an environmental perspective. The results demonstrated that MUD can be successfully valorisated in the manufacture of red stoneware ceramic bodies with similar, or even better technological properties than commercial materials used currently.

O24-4 Impact of seafood consumption before sample donation on urinary and toenail metal levels in workers exposed to heavy metals

Introduction Dietary intake is the main source of exposure to metals in the general population, however, among metal, chemical and mining workers, occupational exposure would be the most important source. Fish and seafood consumption can influence the levels of arsenic and mercury in blood and urine, but little information is available for other metals. We assessed the impact on metal levels of seafood, molluscs and fish consumption (SMFc) before urine and toenails sample donation in a group of exposed workers. Methods Cross-sectional epidemiological study. We measured urinary (As, Ba, Be, Cd, Co, Cu, Hg, Li, Mo, Pb, Se, Sr, Tl, V, W and Zn), and toenail (same plus Al, Cr, Fe, Mn, Ni and U) metal levels. Information on SMFc and urine or toenail levels was obtained from 101 workers from the chemical and metal industry, and from 40 unexposed workers from the services sector. 84% of workers were male. Metal levels were measured using multielemental ICP-MS analysis. We compared the median for each metal between those with and without SMFc (U Mann-Whitney test). We used lineal regression models adjusted for age sex, and industry to assess the association between hours before SMFc and each metal level. Results Urinary arsenic levels were higher among those workers who reported eating seafood or molluscs (102 ppm vs 55.4 ppm; p = 0.042) or fish (109 ppm vs 48 ppm; p = 0.007) 8 hours before sample donation. With respect to toenails, fish consumption was associated to aluminium (17 ppm vs 8.6 ppm; p = 0.012) and beryllium (5 ppb vs 1 ppb; p = 0.017). Arsenic urinary levels were associated with numbers of hours prior to sample collection since latest SMFc (p = 0.001). Conclusion Seafood, molluscs and fish consumption is an important determinant of urinary arsenic levels, but not for other metals among exposed workers to metals.