Table 1

Chemical analysis results of acid-containing wastewater"

Table 2

Chemical analysis results of precipitating agent"

Fig.1

Process flow diagram of two-stage MDEC crystallization"

Fig.2

Schematic diagram of MDEC crystallizer"

Table 3

Experimental results with differenttypes of precipitant"

Fig.3

Effect of seed addition amount on particlesize of first-stage gypsum"

Fig.4

Effect of temperature on particle sizeof first-stage gypsum"

Fig.5

Effect of reaction time on particle sizeof first-stage gypsum"

Fig.6

Effect of stirring rate on particle size of first-stage gypsum"

Fig.7

Effect of aging time on particle size of first-stage gypsum"

Table 4

Effect of different treatment capacity on particle size of gypsum"

Table 5

Effect of different pH in crystal regionon particle size of gypsum"

Fig.8

Particle size of first-stage gypsum testedcontinuously for 48 h"

Fig.9

Chemical analysis results of first-stage gypsumtested continuously for 48 h"

Fig.10

Effect of lime addition on particle size of gypsum"

Fig.11

Effect of reaction pH on particle size of gypsum"

Fig.12

Particle size of second-stage gypsumtested continuously for 48 h"

Fig.13

Chemical analysis results of second-stagegypsum tested continuously for 48 h"

Table 6

Analysis results of first-stage andsecond-stage gypsum"

Fig.14

XRD patterns of first-stage gypsum（a）and second-stage gypsum（b）"

Fig.15

SEM images of first-stage gypsum（a）and second-stage gypsum（b）"

Fig.16

Particle size distribution of first-stage gypsum（a） and second-stage gypsum（b）"

Table 7

Chemical compositions of first-stage and second-stage gypsum"

Table 8

Analysis results of gypsum after drying at 120 ℃"