A well treatment composite comprising a well treatment agent adsorbed onto a water-insoluble adsorbent may be prepared by precipitating the well treatment agent, in the presence of a metal salt, from a liquid while the well treatment agent is being adsorbed onto the water-insoluble adsorbent. After a treatment fluid containing the composite is introduced into a well or a subterranean formation, the well treatment agent is slowly released from the composite. The composite permits a continuous supply of the well treatment agent into a targeted area and is particularly effective in high pH treatment fluids.