SHANGHAI, Mar. 18 (SMM) –Spot aluminum largely traded between RMB 12,870-12,890/mt in Shanghai on Wednesday, discounts of RMB 230-250/mt over SHFE 1503 aluminum contract, versus RMB 12,860-12,880/mt in Wuxi, and RMB 12,880-12,900/mt in Hangzhou. Growing spot discounts widened the room for arbitrage, luring traders in. Processors bought only to need.