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The aim of this study was to geochemically and mineralogically assess materials from two already closed pits. Total testing and leachate testing (Equilibrium Leach Test and Sequential Leach Test) of topsoil, waste stabilized with lime and underlying rock was performed on composite samples. An analysis of underground water from underlying rock was also accomplished. Major pollutants in stabilized waste from investigated locations differ. High total values of some heavy metals in stabilized waste from one of the investigated locations can probably be attributed to high barite content (mercury, zinc and cadmium) and pipe dope (lead). Mercury, zinc and cadmium are enriched in the organic-sulfide fraction that might indicate they are tied up as sulfide impurities in barite. In distilled water lecheate of stabilized waste from this location higher concentrations of Pb, Hg and TOC were observed. In the stabilized waste from the second location high total values of total oils and mineral oils, PAH and BTEX were detected, while distilled water lecheate is enriched with Hg, total oils and mineral oils, AOX and TOC. This investigation shows that stabilization with lime is not always a suitable method for treatment of wastes from the petroleum industry, particularly those that are contaminated with both organic and inorganic contaminants. Proper characterization of the waste material to be processed is needed in order to select the most appropriate method of treatment. Our ongoing research study uses different pretreatment techniques and different absorbents (organophilic clay, calcined siliceous earth, etc.) to preferentially absorb organic contaminants that can be used before stabilization/solidification.

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Exploration and production (E&P) waste generated by the petroleum industry in Croatia from two central oilfield pits (COPs) was investigated in order to (1) examine materials for waste treatment that can preferentially sorb organic contaminants and, in that way, improve the process of stabilization/solidification (S/S), and (2) find field-acceptable methods to reduce the amount of waste to be treated with S/S or some other method. Composite samples from COP Vinkovci were treated in the laboratory with different materials or with combinations of several materials: (a) Cement, (b) organophilic clay, (c) calcined moler clay, (d) lime+organophilicclay+bentonite, (e) cement+organophilicclay+bentonite, (f) lime+calcined moler clay, and (g) cement+calcined moler clay. A sample of E&P waste treated with lime was used for comparison of results. The most successful treatment for the majority of inorganic and organic pollutants was treatment with organophilic clay. Samples treated with organophilic clay release 63 times less total oils, 67 times less mineral oils, 798 times less naphthalene, and 136 times less lead to distilled water than the sample treated with lime. The next most successful material is calcined moler clay. The results clearly show that reduction in hydrocarbon content using some of the field-acceptable methods and detailed chemical analysis of remaining organic and inorganic pollutants must be implemented before selecting the most appropriate method for treatment of technological waste in petroleum industry. A composite sample from COP Žutica was treated in the laboratory using a four-step procedure involving boiling water, condensate, and organophilic clay. Organophilic clay was used because of its ability to sorb hydrophobic pollutants. In the leachate of an E&P waste sample, the lowest values for the majority of inorganic and organic pollutants were observed following the fourth step (treatment with organophilic clay). This is also manifested in the lowest indicator of total discharge (ITD%) values for the fourth treatment step. Considering the concentrations of analyzed parameters in leachates and their ITD% values, the biggest effect for the majority of inorganic and organic pollutants was achieved between the first and the second treatment step. This suggests that treatment with boiling water is the most effective treatment for the majority of inorganic and organic pollutants. Concentrations of benzene, ethylbenzene, toluene, and xylene (BETX) in distilled-water leachate generally increase after each succeeding treatment step. This shows that BETX is added to the E&P waste through condensate addition in the third treatment step.

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