Boron is an essential nutrient for animals and plants, but it can be harmful in excessive levels. In this study, three types of crushed shells (oyster, hard clam and freshwater clam) were pretreated and then reused as mineralizers to remove and recover the boron from concentrated wastewater by using the microwave hydrothermal method. Chemical and physical properties of raw and pretreated crushed shells were determined and compared using SEM, XRD, BET and WD-XRF. Effects of pretreatment method (heated or pyrolysis), particle sizes, initial boron concentrations, reaction times and shells dosages on boron recovery were investigated. The oyster shells pretreated by heat performed better than heated hard clam and freshwater clam shells, and the boron recovery efficiency reached around 95% within 10 min of reaction time. The experimental results indicate that the pretreated oyster shell is an effective mineralizer for removal and recovery of boron from concentrated wastewater. (C) 2011 Elsevier Ltd. All rights reserved.