Leaching and geochemical modelling of a metallurgical slag heap Dr. Mojca Loncnar (mojca.loncnar@acroni.si) Dr. Hans A. van der Sloot, Hans van der Sloot Consultancy, The Netherlands Assist. Prof. Dr. Marija Zupančič, Faculty of Chemistry and Chemical Technology, University of Ljubljana, Slovenia Assist. Prof. Dr. Ana Mladenovič, Slovenian National Building and Civil Engineering Institute, Slovenia Fifth International Slag Valorisation Symposium │ Loncnar M, van der Sloot H.A., Zupančič M., Mladenovič A. 03/04/2017

Outline: Case study: Metallurgical slag heap Javornik, Slovenia Materials Sampling of heap samples Groundwater monitoring Data comparison and geochemical modelling Results and Discussion Batch data pH dependent data (composite sample) Geochemical modelling Comparison batch data, GW data and pH dependent data Conclusions Fifth International Slag Valorisation Symposium │ Loncnar M, van der Sloot H.A., Zupančič M., Mladenovič A. 03/04/2017

Case study: Metallurgical slag heap Javornik near the town of Jesenice in NW Slovenia approx. 3 ha large Landfill area 2 ha approx. 400 000 t metallurgical wastes Operation started in 1987 2009 landfilling stopped 73 % slags from carbon and stainless steel production 19 % EAF and VOD dust 8 % refractory material other wastes 50 m Source: www.google.si/maps Fifth International Slag Valorisation Symposium │ Loncnar M, van der Sloot H.A., Zupančič M., Mladenovič A. 03/04/2017

Sampling of heap samples 11 locations on the metallurgical heap (batch extraction tests + pH dependence test (on composite sample) Sampled at the depth of around 20-30 cm below the landfill surface Sampled at the depth of around 6m below the landfill surface L1 L9 L7 L4 L8 L2 L5 L10 L3 L6 L11 Source: www.google.si/maps Fifth International Slag Valorisation Symposium │ Loncnar M, van der Sloot H.A., Zupančič M., Mladenovič A. 03/04/2017

Groundwater monitoring (years 2011 – 2015) 7 piezometers Twice annually spring, autumn P1 P1 and P2: reference piezometers P4 P2 P3 P7 P5 P6 Fifth International Slag Valorisation Symposium │ Loncnar M, van der Sloot H.A., Zupančič M., Mladenovič A. 03/04/2017

Data comparison and Geochemical modelling The database / expert system LeachXSTM1: Management of data (the pH dependent leaching data, the batch data, the GW data) and vizualization of the calculated and measured results (in MS Excel) Geochemical speciation and chemical reaction/transport modelling: Modelling environment ORCHESTRA The geochemical modelling: Mineral sorption (extended MINTEQ database) Sorption on Fe-oxides (Dzombak & Morel) Sorption on Al-oxide, dissolved organic carbon (DOC) and particular organic carbon (POM) (interaction according to NICA-DONNAN) Multi-element modelling taking into the account all (33) measured elements Fifth International Slag Valorisation Symposium │ Loncnar M, van der Sloot H.A., Zupančič M., Mladenovič A. 03/04/2017

Total chemical composition Chemical composition of the composite landfill sample Chemical composition of the individual landfill samples Sampled at the depth of around 20-30 cm below the landfill surface Sampled at the depth of around 6m below the landfill surface Fifth International Slag Valorisation Symposium │ Loncnar M, van der Sloot H.A., Zupančič M., Mladenovič A. 03/04/2017

Mineralogy (XRD analysis: the composite landfill sample) Fifth International Slag Valorisation Symposium │ Loncnar M, van der Sloot H.A., Zupančič M., Mladenovič A. 03/04/2017

Mineralogy (SEM-EDS: the micrograph of the prehydrated calcium aluminate grain) Reaction rim is composed of C-A-H phase, with the typical microstructure of (prismatic) hexagonal cross section Fifth International Slag Valorisation Symposium │ Loncnar M, van der Sloot H.A., Zupančič M., Mladenovič A. 03/04/2017

One-stage batch test (CEN 12457) Legend: Inert limit for waste Non-hazardous limit for waste Fifth International Slag Valorisation Symposium │ Loncnar M, van der Sloot H.A., Zupančič M., Mladenovič A. 03/04/2017

Modelling of pH dependent data Multi-element modelling taking into the account all (33) measured elements Chemical speciation fingerprint (CFS) used for the speciation modelling of metallurgical slag heap Fifth International Slag Valorisation Symposium │ Loncnar M, van der Sloot H.A., Zupančič M., Mladenovič A. 03/04/2017

Modelling of pH dependent data: major elements Legend: pH-dep. data model pred. L/S = 10 model pred. L/S = 0.3 Major elements dictate the leaching conditions (pH, Eh, conductivity) In the case of many elements the measured conc. at L/S = 10 correspond well with the model prediction Fifth International Slag Valorisation Symposium │ Loncnar M, van der Sloot H.A., Zupančič M., Mladenovič A. 03/04/2017

Modelling of pH dependence data: parameters of environmental concern Legend: pH-dep. data model pred. L/S = 10 model pred. L/S = 0.3 Fifth International Slag Valorisation Symposium │ Loncnar M, van der Sloot H.A., Zupančič M., Mladenovič A. 03/04/2017

Geochemical modelling Calculated speciation in the liquid and solid phases Leaching of CALCIUM at pH > 12 was adequate describe by portlandite, calcite, CSH and CAH c Fifth International Slag Valorisation Symposium │ Loncnar M, van der Sloot H.A., Zupančič M., Mladenovič A. 03/04/2017

Geochemical modelling Calculated speciation in the liquid and solid phases Leaching of CHROMIUM at alkaline pH controlled by Cr substitution as a solid solution in ettringite Fifth International Slag Valorisation Symposium │ Loncnar M, van der Sloot H.A., Zupančič M., Mladenovič A. 03/04/2017

Comparison of the batch and pH dependent data The batch data plot along the pH dependent leaching curve The same solubility controlling phases control leachability In some samples, Ca is affected by carbonation Legend: pH-dependent data batch data (L1-6) batch data (L7-11) Fifth International Slag Valorisation Symposium │ Loncnar M, van der Sloot H.A., Zupančič M., Mladenovič A. 03/04/2017

Comparison of GW data and pH dependent data The GW data showed lower conc. or fall right on the pH dependent curve Not big differences in the conc. between the reference piezometers and other piezometers indicating limited influence of the landfill area on the GW data Legend: pH-dependent data reference piezometers (P1, P2) piezometers 3-7 Fifth International Slag Valorisation Symposium │ Loncnar M, van der Sloot H.A., Zupančič M., Mladenovič A. 03/04/2017

Comparison of the batch, GW data and pH dependent data The main differences between the batch and pH-dependent data, on the one hand, and GW data, on the other hand, is the contact with the landfill material (solubility control), which is absent in the case of GW monitoring Legend: pH-dependent data reference piezometers (P1, P2) piezometers 3-7 batch data (L1-L6) batch data (L7-L11) Fifth International Slag Valorisation Symposium │ Loncnar M, van der Sloot H.A., Zupančič M., Mladenovič A. 03/04/2017

Conclusion The modelling approach used in this study provides benefits for understanding the observed leaching behaviour, which is needed in the case of decisions about future management of waste heap. It can thus form the basis for the projection of the long-term leachate quality of the landfill under changing exposure conditions such as carbonation and oxidation. Bringing together data from various laboratory leaching tests - in particular pH dependence - , field data, and geochemical modelling results, provides a much more complete picture of the release controlling factors in a landfill than can be provided by any single one of these data sources. Fifth International Slag Valorisation Symposium │ Loncnar M, van der Sloot H.A., Zupančič M., Mladenovič A. 03/04/2017

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