Pre-treatment techniques for pre-treating aqueous suspensions including fine solid particles include coarse debris removal prior to a chemical treatment operation. The suspension may include or be mining tailings, which may include mature fine tailings. The mining tailings may be generated from oil sands mining. The pre-treatment may include screening the tailings to remove coarse debris that would interfere with the tailings chemical treatment. The screening may be done by a screening device including a screen having and a collector body receiving the screened fluid. The screening device may include a tank screen with an inclined screen surface or an in-line screen. Several screening devices may be incorporated into a pre-treatment installation to treat parallel streams of tailings. The pre-treatment may be performed to enhance mixing of a flocculent into the screened tailings, followed by flocculation and dewatering of the tailings.