The main site of bicarbonate re-absorption is:
Proximal convoluted tubule is the main site of bicarbonate absorption. About 80 to 90 percent of bicarbonate re-absorption occurs in the proximal tubule. Ref:Textbook of Medical Physiology By Guyton, 10th Edition, Page 353
Proximal convoluted tubule
Distal convoluted tubule
Coical collecting duct
Medullary collecting duct