Qostanay, Kostanai, or Kustanay (all: kŏsˌtənĪˈ) [key], city (1993 est. pop. 228,000), N Kazakhstan, on the Tobol River. It is an agricultural center and producer of chemical fibers. Rich iron deposits are nearby at Rudnyi. The city expanded dramatically in the 1960s as a result of the Virgin Lands campaign.