Fátima Arroyo

Germanium recovery from gasification fly ash: evaluation of end-products obtained by precipitation methods.

In this study the purity of the germanium end-products obtained by two different precipitation methods carried out on germanium-bearing solutions was evaluated as a last step of a hydrometallurgy process for the recovery of this valuable element from the Puertollano Integrated Gasification Combined Cycle (IGCC) fly ash. Since H(2)S is produced as a by-product in the gas cleaning system of the Puertollano IGCC plant, precipitation of germanium as GeS(2) was tested by sulfiding the Ge-bearing solutions. The technological and hazardous issues that surround H(2)S handling conducted to investigate a novel precipitation procedure: precipitation as an organic complex by adding 1,2-dihydroxy benzene pyrocatechol (CAT) and cetyltrimethylammonium bromide (CTAB) to the Ge-bearing solutions. Relatively high purity Ge end-products (90 and 93% hexagonal-GeO(2) purity, respectively) were obtained by precipitating Ge from enriched solutions, as GeS(2) sulfiding the solutions with H(2)S, or as organic complex with CAT/CTAB mixtures and subsequent roasting of the precipitates. Both methods showed high efficiency (>99%) to precipitate selectively Ge using a single precipitation stage from germanium-bearing solutions.

Precipitation of Germanium from Coal Fly Ash Leachates

The valorization of a coal gasification fly ash was studied by leaching the fly ash using different aqueous solutions followed by the subsequent precipitation of the germanium solubilized from the ash. Experimental investigations were focused on the precipitation of a germanium-catechol (CAT) complex with cetyl trimethyl ammonium bromide (CTAB). The influences of pH and amounts of CTAB and CAT on the precipitation yield were investigated. To this aim, a central composite rotatable design and ANOVA Design Expert 7.0.3 Wiley software were employed for experimental design and analysis of the results. Thus, the independent and combined effects of pH, CAT/Ge and CTAB/Ge molar ratios were investigated and optimized using a quadratic mathematical model. The optimum values of these factors were found to be 10, 12, and 4, respectively (in this case, the germanium precipitation yield was 98.8% for water leachates). The precipitation of germanium as a complex compound with CAT and CTAB was found to be selective towards germanium and this element can be effectively separated from As, Mo, Sb, V, or Zn. Total organic carbon in solution was measured to estimate the amounts of CAT and CTAB precipitated with germanium and with the interferences present in aqueous leachates. In addition, thermogravimetric analyses have been performed on the germanium-complex solids as a result of which 600°C was determined as the minimum temperature to completely remove the organic content of the precipitate.

Assessing durability properties of noise barriers made of concrete incorporating bottom ash as aggregates

Abstract This research analyses the durability of a noise barrier using coal bottom ashes as aggregates in a high proportion (80%wt of bottom ash). A concrete noise barrier is composed by a combination of a porous sound absorbing face and a standard concrete in order to increase the mechanical properties of the barrier. The bottom ash was sieved at 2.5 mm, a porous concrete with the coarse fraction of bottom ashes and a standard concrete with the fine fraction of bottom ashes were made. This paper analyses the water absorption, resistance to acid attacks, resistance to sulphate attacks and resistance to freeze-thaw cycles, determining mechanical and acoustical properties of the porous concrete. When the materials are subjected to acid and sulphate attacks, the compressive strength is reduced to 20% and the noise absorption to 40% from initial baseline. When all the materials are subjected to freeze-thaw cycles, a mass loss higher than 15% at 30–40 cycles was observed, the compressive strength of materials with a high particle size drops at 20–30 cycles for natural and bottom ashes aggregates, and the noise absorption of bottom ash materials present a lower drop than natural aggregates.