Research interests within the Environmental Mineralogy Research Group include:

The list below contains short descriptions of our current research topics, while our publications are here.

 

Properties and formation mechanisms of carbonates in lakes

This line of research developed from our interest in Lake Balaton, a large,  shallow lake that has a distinguished place in Hungarian hearts and culture (including science). We study sediment formation in the lake, with a focus on carbonate precipitation. Our mineralogical work resulted in new knowledge on the heterogeneous nucleation of carbonates and freshwater dolomite formation, all of which have some relevance to lake ecology and lake management. Distinct research topics in this theme are the following:

  • Molecular dynamics simulations of the heterogeneous nucleation of calcite from lakewater. We ran calculations for 30 ns with about 2 million atoms both in homogeneous solutions and heterogeneous systems including two types of clay minerals. it was found that ionic clusters form in the bulk solution and then get anchored on the clay surfaces, with montmorillonite being a far more efficient surface than kaolinite. (Researchers involved: Fodor Melinda Fodor, Zoltán Ható, Tamás Kristóf, Mihály Pósfai
  • Experimental precipitation of carbonates in the presence of absence of heterogeneous surfaces. Using an automatic titrator we feed Ca into a carbonate-bearing solution, and measure the dissolved Ca with an ion-selective electrode in order to identify nucleation events and to compare clay-free and clay-containing systems. For studying the precipitated materials, we use TEM. (Researchers involved: Zsombor Molnár, Péter Pekker, Mihály Pósfai)
  • Establishing the "mineral budget" of Lake Balaton – what is the origin of sediment minerals (inlets, precipitation, dry deposition, precipitation from the lake), what is the intensity of distinct sources, and which processes affect the deposition and persistence of various minerals. (Researchers involved: Ágnes Rostási, Kornél Rácz, Melinda Fodor, Boglárka Topa, Tamás Weiszburg, Mihály Pósfai)
  • Carbonate precipitation mediated by algae, studied in lab experiments. The tas is, in fact, the experimental simulation of processes taking place in Lake Balaton but, contrary to the titration experiments above, we also include a biogenic factor, the photosynthesis performed by diatoms. The results could shed light on the temporal fluctuations of precipitation and the effects of algae on polymorph selection. (Researchers involved: Ágnes Rostási, Zsombor Molnár, Kornél Rácz, Edina Lengyel, Mihály Pósfai)
  • Separation of calcite and dolomite using various acid leaching procedures, as a function of grain sizes. There are several established leaching methods for separating carbonate minerals; however, the effects of grain sizes on the efficiency of these techniques has not been systematically studied in some systems. (Researchers involved: Kornél Rácz, Mihály Pósfai)
  • Dolomite precipitation in Lake Fertő (Neusiedlersee). This topic was initiated by Dr. Patrick Meister (U. Vienna). It appears that the very high Mg/Ca ratio in this special lake results in the precipitation of nanoscale ordered dolomite.  Studying cation ordering in this beam-sensitive material is a great challenge and we are pushing the capabilities of our Talos TEM to its limits; as a result, initial observations raise fundamental questions about the precipitation/dissolution of carbonates in a natural environment and about the ordering of cations in carbonates. (Researchers involved: Patrick Meister (U. Wien), Péter Pekker, Zsombor Molnár, István Dódony, Silvia Frisia (U. Newcastle), Mihály Pósfai)
  • Phosphorus in lakewater sediments. This topic was inspired by an algal bloom in Lake Balaton in August 2019, an unexpected event for which a large supply of "internal" phosphorus was necessary. At the moment we are studying the distribution of phosphorus in our lake sediment samples (it is expected to be bound to carbonates and iron oxides). In addition, we plan lab experiments to understand how P is bound to sediment minerals and under what conditions will it be released. (Researchers involved: Kornél Rácz (iron oxides), Zsombor Molnár (carbonates), Péter Pekker, Vera Istvánovics (BME), Mihály Pósfai)

 

Structures and formation of biominerals

We have been involved for more than 20 years in research on magnetic biominerals produced by magnetotactic bacteria, mainly focusing on the special properties (size, structure, composition, magnetism) of magnetite and greigite nanocrystals that formed inside the cells of bacteria (see our list of publications). Recently, partly motivated by our work on lacustrine carbonates, we started to study the interesting nanostructures of carbonate biominerals.

  • Micro- and nanostructures and compositions of fish otoliths. Otoliths are part of the gravity and acceleration-sensing organs of vertabrates and consist mostly of aragonite. We study fish otoliths that grow continuously during the fish's lifetime, producing tree-ring-like structures that can be used as environmental proxies. We wish to understand the effects of environmental factors on the development of mineral structures and compositions. Involved: Zsombor Molnár, Regina Kövér (BSc student), Zoltán Vitál (ÖK BLI Tihany), Mihály Pósfai)
  • Potential dissolution of spent Dreissena shells in Lake Balaton. Two invasive species of Dreissana populate the bottom of the lake. Despite the presence of aragonitic shells, we hardly found any aragonite in the sediment, according to XRD, raising the possibility of the dissolution of spent shells.  We are performing both field and lab dissolution experiments in order to understand the fate of shells. The topic has general relevance for both lake ecology and carbon dioxide fixation. (Involved: Winfred Nyokabi (MSc student), Kornél Rácz, Csilla Balogh (ÖK BLI Tihany), Mihály Pósfai)
  • Nanostructure of mussel shells. While working on the above topic (shell dissolution), we discovered that Dreissena shells contain a variety of planar defects in the structure of aragonite. Our goal is to characterize the types of defects and understand whether they have a biological(?) function. (Involved: Mihály Pósfai, Péter Pekker, István Dódony, Kornél Rácz, Zsombor Molnár)
  • Bullet-shaped magnetite in magnetotactic bacteria. Some strains of magnetotacic bacteria produce magnetite nanocrystals with highly unusual and highly controlled, bullet-shaped morphologies. Despite considerable research, neither the exact crystallographic morphology (faces? curved surfaces? elongations?), nor the growth mechanism is satisfactorily known. We collect bacteria form lakes perform STEM tomography for obtaining the precise morphologies of bullet-shaped magnetosomes and their positions within the cells. (Involved: Péter Pekker, Mihály Pósfai)

 

Synthesis and study of biological and biomimetic magnetic nanostructures

This research theme is based on (a) our previous work on magnetotactic bacteria and (b) the expertise of the UP group led by Prof. Ferenc Vonderviszt in genetically engineering bacterial flagella. We use protein fragments known from magnetotactic bacteria, as well as synthetic polypeptide sequences, to functionalize bacterial filaments for the attachment of magnetite nanoparticles or iron ions from solution.

  • Construction of filamentous magnetic nanostructures by attaching magnetite nanoparticles on genetically engineered (functionalized) bacterial filaments. Currently our most interesting research direction is to quantitatively measure the efficiency of a magnetite attachment on the filaments, and the use of magnetite nanoparticles with distinct morphologies - octahedra and cubes - in order to understand the specific interactions between functionalized filaments and distinct crystal faces. (Involved: Georgina Huszti Nagy, Lejla Papp, Alejandro Gomez Roca (U. Barcelona), Mihály Pósfai, Ferenc Vonderviszt)

 

Properties of individual atmospheric aerosol particles

A long-time research interest of our group is the TEM study of invidiual atmospheric aerosol particles, in order to understand their physical and chemical properties, and the consequences of these properties for atmospheric processes, climate, and health. Our current themes are mostly concerned with anthropogenic particles from combustion sources:

  • Origin and properties of urban magnetic aerosol particles. We compare magnetically separated particles from three sources: the urban atmosphere, exhaust from internal combustion engine vehicles, and vehicle brakes. The significance of the research is the assumed harmful effect of magnetic particles on human health. (Involved: Faizan Ahmad (MSc student), Ilona Nyirő-Kósa, Mihály Pósfai)
  • Individual aerosol particles produced by burning household waste. The burning of household waste is one of the major sources of urban air pollution. Members of the Air Chemistry Research Group (András Hoffer, Ádám Tóth) performed controlled burns of specific waste types, and we study and chracterize the particles produced by distinct fuels. We identify certain properties (soot morphology, composition, presence of specific elements) that can be used as markers for tracing the origin of these particles.  (Involved: Bálint Tóth (BSc student), Mihály Pósfai)
  • Individual particles depositing during Saharan dust episodes. While working on one of the research topics above (mineral budget of Lake Balaton) we collected rainwater over a one-year period and filtered the solid material from it. Among the precipitations events several Saharan dust episodes were identified. We study particles in these samples with the goal of identifying transport pathways for specific particle types and to estimate the mass of dust that deposits in Europe. (Involved: Ágnes Rostási, György Varga (CsFK FTI), Miklós Jakab)