Abstract: Under the background of the national policy of continuously advancing environmental protection and ecological civilization construction,the supply pressure of sandstone aggregate and environmental pressure in traditional sandstone mines are growing,which provides a rare opportunity for the highefficient and comprehensive utilization of waste rock in noncoal solid resources mines.The sandstone aggregate processed by nearore surrounding rocks and the sandstone produced from ore dressing process are available building materials for the markets in Maanshan area,and perfomance better in sales situation.The drydiscarding tailings of fine crushing products from magnetic pulley in Masteel Gaocun ore are good raw materials for the production of building materials.Therefore,scientific determination of MFe grade of drydiscarding waste rock is conducive to the improvement of enterprise economic benefits,the realization of solidwaste resourse efficient utilization and the development goal of building green mines.On the basis of the concept of critical grade in dry discarding process,the relationship between drydiscarding MFe grade with economic benefit and social benefit maximization is demonstrated based on experiment and production practice.The researches suggest that: ① traditional notion which emphasises on loss rate of magnetic iron has not adapted to the new situation.Systematic tests,and economic and environmental benefits analysis should be carried out to determine the drydiscarding critical MFe grade,and the corresponding drydiscarding yield.② The drydiscarding yield of about 10% determined on site is slightly low.When the drydiscarding yield increased from 9.14% to 14.02%,the MFe grade of new lowgrade interlocked increased to 2.87%,bringing about the annual economic benefits of 10.344 milions in the current market conditions.③ Based on the current market conditions and two drydiscarding tests,the critical MFe grade is predicted to be about 4% and the corresponding drydiscarding yield is about 15.5%.The MFe grade of total tailings in drydiscarding operation is about 1.95%,and the MFe loss rate could reach about 2.5%.

Key words: Fine crushing products,Drydiscarding in magnetite separation,Critical grade,Concentration ratio,Sandstone aggregate,Iron concentrate,Synchronous optimization for economics and resourse benefits