Systems and methods for processing a high-lactose aqueous fluid (HLAF), such as permeate from ultrafiltration of whey fluid, are described. The preferred process includes concentrating HLAF containing from about 1 to about 35% solids, wherein at least 50% of the solids are lactose, to form a concentrated HLAF containing from about 45 to about 65% solids; further concentrating the HLAF to form a highly concentrated HLAF containing from about 70 to about 80% solids; cooling the highly concentrated HLAF with a gaseous fluid to create a cooling, concentrating, crystallizing cascade to further concentrate the HLAF to form a partially crystallized HLAF containing from about 78 to about 88% solids; and drying the partially crystallized HLAF in an air-lift dryer to form a product rich in crystalline alpha-lactose monohydrate. An air-lift dryer having diverging sidewalls and methods of using same are also disclosed.