The suspension stage of copper flash smelting was examined by roasting a high arsenic copper smelting feed mixture at 500−900 °C for 0−20 s in nitrogen and air atmospheres. The enrichment of copper, lead, zinc, arsenic, and sulfur in the quenched calcine was determined via chemical analyses. Pyrite and chalcopyrite were the main minerals in the feed mixture, and about 55 wt.% of arsenic was in tennantite. The stability of the feed and the formation of S₂ and SO₂ during roasting were surveyed by thermal analysis combined with mass spectrometry. Selected pure impurity sulfides were studied for reference purposes. Results indicated that arsenic was released more easily in inert atmosphere compared to air, in which oxidation products of sulfides captured the released gaseous arsenic. Kinetics analyses showed that the third-order chemical reaction and three-dimensional diffusion models were found as the most suitable mechanism functions of arsenic volatilization in inert and air atmospheres, respectively.