A. Garralón

The impact of the Aznalcóllar mine tailing spill on groundwater

As a consequence of a mine tailing dam collapse on the 25th April 1998, more than 4000 ha of the Guadiamar riverflat and farmlands were flooded by 4 hm3 of sulphide slurry. A number of open wells (12 of the 47 analyzed) were also flooded and the water was contaminated. Before the spill, the groundwater in the aquifers was of calcium-carbonate and calcium-sulphate type, with moderate mineralisation and near neutral pH. With the exception of some of the wells close to the mine, this groundwater had a low concentration of the metals associated with the Aznalcóllar mine. After the flood the following metals had anomalous concentrations in well water: Zn, Mn, Pb, Co, Cd and Tl. Of these, Zn seems to be the best tracer of the contamination, owing to its high concentrations. During the 5 months following the spill, water from the unflooded wells did not show an increase in metal concentration. Apart from some exceptions in August, the metal concentration in the affected wells showed a progressive decrease reaching levels closer to those in the wells free from contamination. Nevertheless, in the following dry seasons the draw-down of the water level may lead to exposure and weathering of sulphides in the wells, which could cause an increase in pollution. Therefore, thorough cleaning of all highly contaminated wells is strongly recommended.

The geochemical aspects of toxic waters retained in the Entremuros area (Spain)

Abstract Two walls were built, in order to retain approximately 2 Hm 3 of toxic water from the Aznalcollar mine-tailing dam. This water accumulated in a channel (approx. 10 km long and 1 km wide) in the lower part of the Guadiamar River (Entremuros) and was sampled during the first week of June 1998. The results indicate that the chemistry of the samples located at the northern part of the channel is controlled by a mixture of two processes — dilution of polluted water by the Guadiamar River and precipitation; consequently, medium or low concentrations of toxic elements were measured. The solid phases that determine the chemical equilibrium are calcite, smithsonite and gypsum. On the other hand, the most polluted zone is located to the south of the area studied. These waters are more acidic, and hence, have a higher content of dissolved heavy metals. For example, the Zn concentration is three orders of magnitude greater than in unpolluted samples. Prior to their flushing to the Guadalquivir River, the Entremuros waters were chemically neutralised with Na 2 CO 3 and NaOH. This neutralisation process was modelled and the results were compared with the analytical data obtained during the sampling campaign. The natural removal of heavy metals, which was observed in the waters, was produced by an increase of pH due to a strong evaporation in the zone. This removal produced the precipitation of hydroxides and carbonates of heavy metals, a process, which was also clearly shown in the modelling.

Factors that control the geochemical evolution of hydrothermal systems of alkaline water in granites in Central Pyrenees (Spain)

La evolucion geoquimica de las soluciones de los sistemas hidrotermales de Caldas de Boi, Arties, Tredos y Les, situados en el Pirineo Central (Spain), muestra diferencias reflejadas en la concentracion de solidos disueltos y en la presencia de una situacion de equilibrio o desequilibrio en profundidad de las soluciones respecto a la albita. La datacion (14C) de las aguas pertenecientes a los distintos sistemas hidrotermales ha puesto de manifiesto que el tiempo de residencia no es el factor de control determinante de las diferencias existentes en el grado de evolucion geoquimica alcanzado por las mismas, teniendo que contemplarse otro tipo de factores relacionados con la cinetica de disolucion de los minerales, como responsables de estas diferencias. El analisis de la influencia de los principales factores que controlan la tasa de disolucion de los minerales y, mas en concreto, de los feldespatos, muestra como las diferencias de temperatura de las soluciones en profundidad son capaces de justificar el distinto grado de evolucion geoquimica, incluso en soluciones con tiempos de residencia muy similares.

A comparative study of ultrafiltration and physicochemical process as pretreatment of seawater reverse osmosis

Abstract The effectiveness of two pretreatments for open intake seawater reverse osmosis (RO), aerated spiral wound ultrafiltration (ASWUF) and physicochemical (PC) pretreatment, were evaluated. Their efficiency in removing particulate materials was assessed by SDI, turbidity and Particle Size Distribution. Aerobic bacteria levels indicated the effectiveness of bacterial removal. Organic matter was characterized by TOC and UV254. The apparent molecular weight (MW) distribution of organic matter was determined by centrifugal ultrafiltration fractionation and the effect of pretreated effl uent on seawater RO flux decline was evaluated by a bench-scale test. Both pretreatments lowered feed water SDI to 2 and turbidity to 0.4 NTU and were highly efficient in removing particles larger than 1 μm. In general, ASWUF was more effective than PC, although PC removed TOC more effi ciently. For both pretreatments, TOC fractions with a MW of under 3 kDa remained in treated water. Both pretreatments made effl uents of e...