Titration Curves: A Useful Instrument for Assessing the Buffer Systems of Acidic Mining Waters (10 pp)

Background, Aims and Scope The acidification of mine waters is generally caused by metal sulfide oxidation, related to mining activities. These waters are characterized by low pH and high acidity due to strong buffering systems. The standard acidity parameter, the Base Neutralization Capacity (BNC) is determined by endpoint titration, and reflects a cumulative parameter of both hydrogen ions and all buffering systems, but does not give information on the individual buffer systems. We demonstrate that a detailed interpretation of titration curves can provide information about the strength of the buffering systems. The buffering systems are of importance for environmental studies and treatment of acidic mining waters. Methods Titrations were carried out by means of an automatic titrator using acidic mining waters from Germany and Canada. The curves were interpreted, compared with each other, to endpoint titration results and to elemental concentrations contained therein. Results and Discussion The titration curves were highly reproducible, and contained information about the strength of the buffer systems present. Interpretations are given, and the classification and comparison of acidic mining waters, by the nature and strength of their buffering systems derived from titration curves are discussed. The BNC-values calculated from the curves were more precise than the ones determined by the standard endpoint titration method. Due to the complex buffer mechanisms in acidic mining waters, the calculation of major metal concentrations from the shape of the titration curve resulted in estimates, which should not be confused with precise elemental analysis results. Conclusion Titration curves provide an inexpensive, valuable and versatile tool, by which to obtain sophisticated information of the acidity in acidic water. The information about the strength of the present buffer systems can help to understand and document the complex nature of acidic mining water buffer systems. Finally, the interpretation of titration curves could help to improve treatment measurements and the ecological understanding of these acidic waters.     

Electrocoagulation process for the treatment of metal-plating wastewater: Kinetic modeling and energy consumption

The wastewater from industrial area was treated by EC via Fe and Al electrodes. Cu, Ni, Cr and Zn were highly removed at the first minutes, simultaneously. Pseudo-2nd-order was found to be more suitable for kinetics. Adsorption capacities based on kinetic modeling were observed as Cr>Cu>Ni>Zn. The chemical cost in the case of pH adjustment after EC was less as 3.83 $/m³. It is known that wastewater produced by the metal-plating industry contains several heavy metals, which are acidic in nature and therefore toxic for the environment and for living creatures. In particular, heavy metals enter the food chain and accumulate in vital organs and cause serious illness. The precipitation of these metals is mostly achieved by pH adjustment, but as an alternative to this method, the electrocoagulation process has investigated in this study using iron and aluminum electrodes. The effects of the pH adjustment on removal before and after the electrocoagulation process were investigated, and cost analyses were also compared. It was observed that a high proportion of removal was obtained during the first minutes of the electrocoagulation process; thus, the current density did not have a great effect. In addition, the pH adjustment after the electrocoagulation process using iron electrodes, which are 10% more effective than aluminum electrodes, was found to be much more efficient than before the electrocoagulation process. In the process where kinetic modeling was applied, it was observed that the heavy metal removal mechanism was not solely due to the collapse of heavy metals at high pH values, and with this modeling, it was seen that this mechanism involved adsorption by iron and aluminum hydroxides formed during the electrocoagulation process. When comparing the ability of heavy metals to be adsorbed, the sequence was observed to be Cr>Cu>Ni>Zn, respectively.     

On the Estimation of Dispersal Kernels from Individual Mark-Recapture Data

We present a new method for estimating a distribution of dispersal displacements (a dispersal kernel) from mark-recapture data. One conventional method of calculating the dispersal kernel assumes that the distribution of displacements are Gaussian (e.g. resulting from a diffusion process) and that individuals remain within sampled areas. The first assumption prohibits an analysis of dispersal data that do not exhibit the Gaussian distribution (a common situation); the second assumption leads to underestimation of dispersal distance because individuals that disperse outside of sampling areas are never recaptured. Our method eliminates these two assumptions. In addition, the method can also accommodate mortality during a sampling period. This new method uses integrodifference equations to express the probability of spatial mark-recapture data; associated dispersal, survival, and recapture parameters are then estimated using a maximum likelihood method. We examined the accuracy of the estimators by applying the method to simulated data sets. Our method suggests designs for future mark-recapture experiments. Received: January 2004 / Revised: July 2005