Chloride salts of certain rare earth elements have beneficial effects as clarifying agents in the primary treatment of wastewater. Disclosed herein are methods for treating wastewater comprising dosing wastewater, as part of a primary treatment system, with a clarifying agent of chloride salts of rare earth elements, either individually or mixtures. The rare earth clarifying agents are added or dosed at any point upstream of the primary treatment operation, within the primary treatment operation, or both upstream of and within the primary treatment operation. Also disclosed herein are clarifying agents for use in the primary treatment of wastewater comprising an aqueous solution of chloride salts of the rare earth elements.