According to conveyorbeltguide.com
(yes, that is a real website) the longest conveyor belt in the World is found in Western Sahara. Well, technically, it is actually 11 belts making up the world's longest conveyor belt system. Running for no less than 98 km (61 miles) the belts have transported phosphate rock and dust from the interior’s mines to a specially made port for the past 30 years. The system starts in Boucraa, south-east of Laayoune, and reaches the coast at the harbour south of Laayoune Plage. If you are travelling in the region, you will inevitably cross the belt on the main highway running north-south or drive parallel with it between Laayoune and Smara. Should you be interested, but not be willing to make the trip to West Sahara is the belts clearly viable on Google Maps: look for the long, straight, white line in the sand, phosphate dust blown off the conveyor belt have left a clear mark, stretching for tens of kilometres.