Exploitation of lignite within the area of Muskau Arch, carried out from the mid-nineteenth century, contributed to the transformation of the natural environment and changes in water regime. In the post-mining subsidences pit lakes were formed. The chemical composition of waters is a consequence of the intensive weathering of pyrite (FeS2), which is present in Miocene lignite-bearing rock forming the embankments of the lakes. This process leads to the formation of Acid Mine Drainage (AMD) and finally acidification of lake waters.

This paper presents results of the identification of hydrogeochemical processes affecting the chemistry of waters from these reservoirs carried out using the speciation and statistical (cluster and factor) analyses. Cluster analysis allowed to separate from the analyzed group of anthropogenic reservoirs 7 subgroups characterized by a similar chemical composition of waters. The major processes affecting the chemistry of waters were identified and interpreted with help of factor and speciation analysis of two major parameters (iron and sulfur).

The adsorption of lead ions onto a zeolite bearing tuff (stilbite) from synthetic acid aqueous solution and

acid mine drainage taken from Sasa mine, Macedonia, is elaborated in this paper. The results present that adsorption

occurs effi ciently in both of cases.

The physical and chemical properties of the used natural material, zeolite bearing tuff, are characterized by X-ray

diffraction, scanning electron microscopy, energy dispersive spectroscopy. The concentration of metal ions in solution

before and after treatment is obtained by AES-ICP.

The effectivity of zeolite bearing tuff is determined through a series of experiments under batch conditions from

single ion solutions, whereby the main parameters are the effects of initial pH of solution, mass of adsorbent, initial

metal concentration in solution, contacting time and competing cations. The maximum capacity of zeolite bearing tuff

for removal of lead ions from solution is determined by equilibrium studies.

The experimental obtained data are fi tted with Freundlich and Langmuir adsorption models. The experimental

data are better fi tted with Langmuir adsorption isotherm.

Zeolite bearing tuff is effective adsorbent for treating acid mine drainage. The results showed that 99% of lead ions

are removed from acid mine drainage, i.e. the concentration of lead ions from 0.329 mg/dm3

decrease to 0.002 mg/dm3

.

The pH value of acid mine drainage from 3.90 after treatment with zeolite bearing tuff increases to 5.36.

Acid mine drainage has always been of global concern, primarily due to its low pH, high concentration of heavy metals and toxic substances, and serious impact on the surrounding environment and ecology of mines. However, the research progress and hotspots in this field of acid mine drainage processing are still unclear. To better understand the research hotspots and trends of acid mine drainage processing from 2004 to 2023, we used CiteSpace bibliometric software to visually analyze 1142 English-language research articles and reviews from the Web of Science core database. Results indicated that this field has received increas-ing attention from researchers worldwide, especially since 2017. The USA and China stand out as major contributors, yet their international collaboration doesn't match South Africa robust partnerships. Strengthening cooperation with other nations should be a priority for both the USA and China. The University of Quebec and University of South Africa were the most production institution. Vhahangwele Masindi from South Africa was the most active author. The top two core journals in this field were Science of the Total Environment and Water Re-search. Additionally, through keyword co-occurrence, clustering, and burst analysis, it is evi-dent that research on heavy metal mechanisms and resource recovery will be the future re-search hotspots in this field of acid mine drainage. This study provides researchers with an opportunity to understand the hotspots and trends in acid mine drainage research from a bibliometric perspective, and serves as a reference for future studies.