How to separate sulfur and carbon powders?
Two possibilities:


Distillation: Sulfur has the comparatively low boiling point of 718 K ​(445 °C). Heating in apparatus not affected by sulfur (which leaves out iron) will leave behind the carbon. This is, after all, how sulfur winds up at volcanic vents, where it is harvested. You might even create a retort out of concrete, which would simulate volcanic rock.
Sulfur is somewhat soluble in toluene and in carbon disulfide, but both are toxic and flammable, with $\ce{CS2}$ being particularly easy to ignite. These are not safe to use without proper training and equipment.