Probably the biggest financial failure of Edison's career was the magnetic iron-ore separator. The idea, which Edison's laboratory experimented with during the 1880s and 1890s, was to use magnets to separate iron ore from unusable low-grade ores. This would mean that abandoned mines could be profitable once again through the extraction of iron from sand at the sites -- at the time, iron ore prices had risen to unprecedented heights.
Edison's laboratory was preoccupied with developing a magnetic iron-ore separator and putting it to practical use. He acquired rights to 145 abandoned mines and set up a pilot project at the Ogden mine in New Jersey. Edison poured money into the project, gradually selling most of his interest in the General Electric Company to pay for his work. But the engineering problems were never worked out and the price of iron ore fell, leading Edison to finally abandon his iron-ore separator.