Thermal metamorphism of original coal adjacent to burning centers in coal waste heaps is a common phenomenon, and semi-coke and coke are formed during this process. In this study, changes taking place during the pyrolysis of both organic and inorganic constituents of coal in burning heaps are interpreted, and the volatility of major and trace elements is assessed. Experimental pyrolysis of bituminous coal from the coal and uranium Novátor Mine (Czech Republic) was carried out at temperatures of 200 °C, 500 °C, 700 °C and 900 °C. Changes occurring at various temperatures of pyrolysis in the coal matrix were studied by methods of coal petrography, organic and inorganic geochemistry. Due to the high contents of sulfides of Fe, Cu Zn and Pb in coal, changes in their chemical composition which occur during their melting were also studied.

The results showed that with rising temperature the amount of gas produced during the pyrolysis increased significantly while the amount of released nitrogen from coal organic substance and CO₂ decreased and, conversely, the H₂ content was increasing significantly. The largest amount of tar originated at a temperature of 500 °C. Coke and semi-coke appeared in the solid residue already at a temperature of 500 °C and, as the temperature increased, its porosity and optical reflectance were gradually increasing. The results of gas chromatography/mass spectroscopy (GC/MS) showed that the pyrolysis was associated with a rapid decline in the extractability of solid products of pyrolysis. The maximum concentration of polycyclic aromatic hydrocarbons (PAHs) in coke was recorded at 500 °C (28.5 rel.% of identified compounds), and then dropped to 11 rel.% at 900 °C.

The concentration of Hg in the solid residue after the pyrolysis declined significantly even at temperatures of <500 °C. At higher temperatures, apart from Hg, the amount of In, Sb, Tl, Zn, As, Mo, Sn, Pb, Se, Hg and Cd in the pyrolysis residuum gradually decreased, which corresponds to the presence of sulfides of the above elements in the mats of coal fire gas minerals (CFGM) on the surface of many burnt coal heaps.

Galena was partially melted during the pyrolysis already at a temperature of 700 °C to form metallic Pb. However, a significant increase in the volume of melts occurred when the temperature reached 900 °C with the formation of mineral assemblage consisting of galena – metallic Pb – pyrrhotite – sphalerite – intermediate Cu-Fe solid solution phase (iss) – bornite. Consequently, the melting of sulfides during the pyrolysis can be one of the reasons for high volatility of some chalcophile elements in the processes of coal pyrolysis in burning heaps.

废煤堆中靠近燃烧中心的原煤发生热变质是普遍现象，在此过程中会形成半焦和焦炭。在这项研究中，解释了燃烧堆中煤的有机和无机成分热解过程中发生的变化，并评估了主要和微量元素的挥发性。在 200 °C、500 °C、700 °C 和 900 °C 的温度下对来自煤和铀 Novátor 矿（捷克共和国）的烟煤进行了实验热解。通过煤岩学、有机和无机地球化学等方法研究了煤基质在不同温度下热解发生的变化。由于煤中Fe、Cu、Zn和Pb的硫化物含量高，因此还研究了它们在熔化过程中化学成分的变化。

结果表明，随着温度升高，热解过程中产生的气体量显着增加，而煤有机物和CO ₂释放的氮量减少，反之，H ₂含量显着增加。最大量的焦油产生于 500 °C 的温度。焦炭和半焦炭在 500 °C 的温度下已经出现在固体残渣中，并且随着温度的升高，其孔隙率和光反射率逐渐增加。气相色谱/质谱 (GC/MS) 的结果表明，热解与热解固体产物的可萃取性迅速下降有关。焦炭中多环芳烃 (PAH) 的最大浓度在 500 °C 时记录（占已识别化合物的 28.5 rel.%），然后在 900 °C 时降至 11 rel.%。

即使在 <500 °C 的温度下，热解后固体残留物中的汞浓度也显着下降。在较高温度下，除 Hg 外，热解残渣中 In、Sb、Tl、Zn、As、Mo、Sn、Pb、Se、Hg 和 Cd 的含量逐渐减少，这对应于上述元素的硫化物的存在在许多燃烧过的煤堆表面的煤火气矿物（CFGM）垫中。

方铅矿在热解过程中已经在 700 °C 的温度下部分熔化，形成金属 Pb。然而，当温度达到 900 °C 时，熔体体积显着增加，形成由方铅矿 - 金属 Pb - 磁黄铁矿 - 闪锌矿 - 中间 Cu-Fe 固溶体相（iss ） - 斑铜矿组成的矿物组合。因此，热解过程中硫化物的熔化可能是煤堆燃烧热解过程中某些亲硫元素挥发性高的原因之一。