Conference Papers

Sulphate is the specific anion present in the acid rock drainage (ARD). Although sulphate is considered benign or with low toxicity, some countries have set limits for the wastewater discharged to natural receivers, often 500 mg/L or 600 mg/L. By conventional treatment of the ARD with calcium hydroxide, some gypsum can precipitate, depending on the ARD initial sulphate content, but the conformity for sulphate will not be achieved, because the concentration correlated to gypsum solubility exceeds the limit value by roughly three times. An experimental study has been carried out to assess sulphate precipitation via ettringite process from acid rock drainage originating from closed non-ferrous mine site in the North Romanian mining area. Tests for sulphate precipitation, using monocalcium aluminate cement as source of reactive aluminium for the ettringite formation, showed important differences regarding sulphate precipitation yield between batch and continuous flow reaction systems, due to reaction system itself. For continuous stirred tank reactor system (CSTR) a total space-time of 2.6 h is required when operating with cement dose equivalent to 265 mg Al for 1 g sulphate in order to safe meet the sulphate discharge limit of 600 mg/L for mine water with initial c(SO42-) = 2650 mg/L and at a temperature of 15 oC.

The rapid population increase and subsequently the increase of anthropogenic activities have a growing impact on the environment. More than fifty thousand chemicals are regularly introduced into the environment affecting also the aquatic system, especially the groundwater system, which represents the world’s larger freshwater reservoir. It is highly important to find an efficient biotechnological solution for wastewater treatment and the microalgae-bacteria granular system offers a better alternative solution.

The effects of the interferents on determination of Cr species via stripping voltametry were evaluated. The method uses a hanging Mercury drop electrode (HMDE) as working electrode. The electrochemically active specie is Cr(VI). In order to determine the Chrome species, Cr (VI) will be determined first. Then, the inactive specie Cr(III) is oxidized at Cr(VI) and thus the total Cr will be determined. By the difference between total Cr and Cr(VI), Cr(III) is determined. In order to analyze the influence of the interferents on the determination of Chrome(VI) – the electrochemically active specie –, the calibration curve on the 0,2-1μg/l domain was created, and then a known concentration of analyte was added. After these stages, the interferent was added in different concentrations, to study its effect on the determinations, by calculating the recovery performance. This procedure was applied for all studied interferents. The interferents found in the determination of Chrome species through voltammetric methods are: the metallic ions that can be reduced and accumulated on the hanging Mercury drop electrode, where some metals can form inter-metallic compounds with Chrome; compounds that can form complexes or precipitates with it; as well as compounds with tensioactive properties which can be adsorbed on the surface of the electrode, thus influencing its activity. In the case of surface or underground waters, it was noted that, in the process of determining the Chrome species through the techniques of stripping voltammetry, the following metals can interfere: Cu, Pb, Fe, Zn, Mn, Co, as well as tensioactive compounds. We studied and quantified the concentrations of interferents from which strong perturbations appear in the determinations, as well as the analyte/interferent ratio. Therefore:  Fe interferes in the correct evaluation of the result at concentrations higher than 500μg/l concentration corresponding to a Cr(VI):Fe ratio of 1:1000;  Zn, Mn, Cu, Ni, Co show interferences over values of 1000 μg/l corresponding to a Cr(VI):Metal ratio of 1:2000;  The tensioactive compounds present significant interferent effects. This concentration corresponds to a Cr(VI) ratio: tensioactive compounds of 1:6000.