In order to purify phosphoric acid hemihydrate (H3PO4·0.5H2O) crystal further, the effects of sweating time and sweating temperature on purification are investigated in a dry-sweating process. Experimental results indicate the content of Mg, As, Sb and Pb in the H3PO4·0.5H2O crystal decreases with increasing sweating time and sweating temperature during sweating process and show the same tendency to decrease with time at different sweating temperatures. The purification rate coefficients of H3PO4·0.5H2O crystals for Mg, As, Sb and Pb are determined. They increase with an increase in sweating temperature. The Arrhenius equation can be successfully used to describe the relationship between the purification rate coefficient and the absolute sweating temperature. The activation energy of sweating for Mg, As, Sb and Pb in the H3PO4·0.5H2O crystal are calculated using these experimental data. These values for Mg, As, Sb and Pb are 130.13, 193.59, 98.51 and 102.29 kJ mol−1, respectively.