Table 1. Experimental factors.

Factors		(−)	0	(+)
A	pH	2	4	6
B	Temperature (°C)	15	30	45
C	Initial concentration of metal ions (mg/L)	10	30	50
D	CaCl2 (mmol/L)	10	55	100
E	HA (mg/L)	1	5.5	10