Abstract: A bentonite clay-based polymerization catalyst is manufactured by adhering together a plurality of smaller acid-activated bentonite clay particles, using a strong mineral acid, such as H.sub.2 SO.sub.4, as a binder. An acid-activated bentonite clay having a particle size below about 60 mesh, U.S. Sieve Series, preferably calcium bentonite, having calcium as a predominant exchangeable action, is mixed with a strong mineral acid, preferably H.sub.2 SO.sub.4, and water to form the catalyst. The mixture is subjected to intensive mixing, curing and drying to form strong particles capable of grinding to a desired particle size distribution, e.g., -6 mesh to +60 mesh, U.S. Sieve Series, to form the catalyst. Fines resulting from the grinding step are completely recycled to the intensive mixing stage of the process to achieve 100% yield. Some adjustment of acid content of the mix may be needed to take into account the acid carried into the mix by recycled fines.