ABSTRACT
The present study focuses on the geochemistry of large phosphogypsum deposits in Huelva (SW Spain). Phosphogypsum slurry waste from fertiliser production was disposed in large ponds containing aqueous waste (i.e. brines) and exposed to weathering. These evaporation ponds were found to be dynamic environments far from attaining steady state conditions where a number of trace pollutants are subjected to temporal variations in response to changing environmental conditions. Chemical, mineralogical and morphological data were used to improve our understanding on the dynamics of a large number of elements in the phosphogypsum-brine-evaporation deposits system. Weekly sampling of brines over the course of 1â¯yr indicated a substantial enrichment in potentially harmful elements (e.g. As, Cr, Cu, F, Ni, U, V, Zn) present in time-dependent concentrations. The evaporation deposits formed multi-layered precipitates of chlorides, sulphates, phosphates and fluorides containing a large number of pollutants in readily soluble forms. The precipitation sequence revealed a time-dependent composition reflecting alternating precipitation and re-dissolution processes associated with seasonal changes in the local weather conditions. Concatenation of precipitation/re-dissolution stages was found to progressively enrich the brines in pollutants. These findings were supported by the observations from a tank experiment simulating the phosphogypsum-brine-evaporation deposits system under laboratory conditions. Given the substantially high concentrations of pollutants present in mobile forms in the brine-salt system, actions to abate these compounds should be implemented.
ABSTRACT
The Israeli quarry industry produces 57 Mt of raw material and â¼4-6Mt of associated sub-economical by-products annually. These sub-economical quarry fines are not used because production and transportation costs considerably exceed their retail value. Therefore these by-products, are stored in large piles of fine grain size particles, create environmental risks to their surrondings. This paper evaluates the possibility of mixing the sub-economical quarry by-products of two Israeli quarries with sub-economical Class F coal fly ash (<20wt.% CaO) to form an economical aggregate sand substitute to be used as a concrete filler product. To study the feasibility of the aggregate as partial substitute to sand in concrete several analyses, including leaching experiements (EN12457-2), analytical techinques (SEM-EDX, ICP-MS, ICP-AES, and XRD), as well as an analysis of the mechanical and chemical properties of the concrete aggregate (strength, workability, and penetration) were performed. Scrubbing quarry waste with coal fly ash was found to be very effective for reducing the leaching rate of potentially harmful trace elements. In addition, adding fly ash with quarry fines as partial substitute to sand enhanced the performance of the concrete mixture and the properties of the fresh and harden concrete.
ABSTRACT
Coal power plants are producing huge amounts of coal ash that may be applied to a variety of secondary uses. Class F fly ash may act as an excellent scrubber and fixation reagent for highly acidic wastes, which might also contain several toxic trace elements. This paper evaluates the potential of using Class F fly ashes (<20% CaO), in combination with excessive fines from the limestone quarry industry as a fixation reagent. The analysis included leaching experiments (EN12457-2) and several analytical techniques (ICP, SEM, XRD, etc.), which were used in order to investigate the fixation procedure. The fine sludge is used as a partial substitute in concrete that can be used in civil engineering projects, as it an environmentally safe product.
