Thallium mobility in mining wastes at the Crven Dol locality, Allchar deposit, North Macedonia
Authors: Đorđević Tamara , Kolitsch Uwe , Drahota Petr , Knappová Magdaléna , Majzlan Juraj , Kiefer Stefan , Mikuš Tomáš , Tasev Goran , Serafimovski Todor , Boev Ivan , Boev Blažo 
Published: March 2020

&lt;p&gt;In order to better understand the environmental behaviour of thallium, we have chosen the abandoned As&amp;#8211;Sb&amp;#8211;Tl&amp;#8211;Au Allchar deposit (North Macedonia) with unique mineral composition and high thallium grades of the ore. We used pore water analyses, selective extractions, single-crystal and powder X-ray diffraction (PXRD), SEM-EDS, electron microprobe analysis (EMPA), and Raman spectroscopy to determine the distribution and speciation of thallium in waste dump material at the Tl-rich Crven Dol locality in the northern part of the Allchar deposit.&lt;/p&gt;&lt;p&gt;PXRD studies showed that the various solid waste samples are comprised mostly of carbonates (dolomite and calcite), gypsum, quartz, muscovite, kaolinite-group minerals followed by orpiment, realgar, pyrite, marcasite, lorandite, and various iron and calcium arsenates and iron (hydro)oxides, both amorphous and crystalline. Raman spectra, SEM-EDS and EMPA also showed the presence of Ca-Fe-, Ca-Mn-, and Ca-Mg-arsenates.&lt;/p&gt;&lt;p&gt;The main primary source of Tl in the waste is lorandite (TlAsS&lt;sub&gt;2&lt;/sub&gt;), which occurs as prismatic crystals and anhedral grains up to 1 mm and is frequently intergrown with realgar. Other Tl sources, included in either realgar or orpiment, are minor Tl sulphosalts such as fangite (Tl&lt;sub&gt;3&lt;/sub&gt;AsS&lt;sub&gt;4&lt;/sub&gt;), raguinite (TlFeS&lt;sub&gt;2&lt;/sub&gt;), picotpaulite (TlFe&lt;sub&gt;2&lt;/sub&gt;S&lt;sub&gt;3&lt;/sub&gt;) and jankovi&amp;#263;ite (Tl&lt;sub&gt;5&lt;/sub&gt;Sb&lt;sub&gt;9&lt;/sub&gt;(As,Sb)&lt;sub&gt;4&lt;/sub&gt;S&lt;sub&gt;22&lt;/sub&gt;). The Tl dissolved during weathering is precipitated as micaceous subparallel crystals of poorly crystalline to amorphous thallium arsenates (representing previously unknown mineral species), forming porous aggregates up to 100 &amp;#181;m. These Tl arsenates are intergrown with dolomite and Ca-Fe-arsenates and appear as two chemically different phases. The first, more common phase shows a variable Tl:As ratio ranging from ca. 2.1 to 4.1 and a variable Ca content (2.2 to 4.1 at.%). In the second, Tl-richer phase, the Tl:As ratio varies from ca. 5.1 to 8.4. Raman spectra of the Tl arsenates display broad bands and may be divided in the fingerprint region into two relevant ranges, 350&amp;#8211;600 and 700&amp;#8211;900 cm&lt;sup&gt;&amp;#8722;1&lt;/sup&gt;, both attributed to arsenate tetrahedral complexes showing As&amp;#8211;O(&lt;em&gt;X&lt;/em&gt;) symmetric stretching with &lt;em&gt;X&lt;/em&gt; = H&lt;sup&gt;+&lt;/sup&gt; or H&lt;sub&gt;2&lt;/sub&gt;O.&lt;/p&gt;&lt;p&gt;Another relatively common Tl precipitate is dorallcharite [TlFe&lt;sup&gt;3+&lt;/sup&gt;&lt;sub&gt;3&lt;/sub&gt;(SO&lt;sub&gt;4&lt;/sub&gt;)&lt;sub&gt;2&lt;/sub&gt;(OH)&lt;sub&gt;6&lt;/sub&gt;], crystallizing in the form of tiny, well-formed platelets that are grouped into aggregates up to 400 &amp;#181;m in size. Tl is also accumulated in (probably cryptomelane-type) Mn oxides (up to 3.6 at.%), pharmacosiderite (up to 0.9 at.%), and jarosite (up to 0.9 at.%).&lt;/p&gt;&lt;p&gt;The pore water contained high aqueous concentrations of Tl (up to 660 &amp;#956;g&amp;#183;L&lt;sup&gt;&amp;#8722;1&lt;/sup&gt;) and As (up to 196 mg&amp;#183;L&lt;sup&gt;&amp;#8722;1&lt;/sup&gt;). Although these concentrations are low with respect to their total concentrations in the solid phase (Tl: 0.07-1.44 wt. %; As: 0.72-8.67 wt. %), mild extractions (ammonium nitrate and phosphate) mobilized up to 44% of the total Tl and 23% of the total As, indicating that a large amount of these toxic elements is bound weakly (sorption) to solids and can be easily mobilized into the pore water.&lt;/p&gt;&lt;p&gt;Financial support of the Austrian Science Fund (FWF) [P 30900-N28] is gratefully acknowledged.&lt;/p&gt;