Modified resins are disclosed for removing a wide variety of solids and/or ionic species from the liquids in which they are suspended and/or dissolved. These modified resins are especially useful as froth flotation depressants in the beneficiation of many types of materials (e.g., mineral and metal ores), including the beneficiation of impure coal comprising clay impurities, as well as in the separation of valuable bitumen from solid contaminants such as sand. The modified resins are also useful for treating aqueous liquid suspensions to facilitate the removal of solid particulates, as well as the removal of metallic ions in the purification of water. The modified resins comprise a base resin that is modified with a coupling agent, which is highly selective for binding to solid contaminants and especially siliceous materials such as sand or clay.