Question: Were trade dollars ever used as money in the United States or were they all exported?
Answer: The vast majority of circulation strike trade dollars, minted 1873-1878, were exported to China. However, they were legal tender in the United States until this provision was repealed on July 22, 1876. Previous to the repeal, many of them did circulate in America, typically at a premium in relation to “greenback” currency.
The Coinage Act of 1965 made the trade dollar legal tender once again, but by that time who would want to spend one, considering their numismatic appeal and value.