UPDATE 1-Ritchie Bros to buy U.S. e-commerce site IronPlanet for $758 mln

Aug 29 (Reuters) - Canadian industrial auctioneer Ritchie Bros Auctioneers Inc said it will buy IronPlanet, a privately held U.S. e-commerce site for used equipment, for about $758.5 million, as it looks to diversify its portfolio.