Aluminum hydroxide crystallization from aluminate solution using carbon dioxide gas: Effect of temperature and time

Carbonation of Sodium Aluminate/Sodium Carbonate Solutions for Precipitation of Alumina Hydrates—Avoiding Dawsonite Formation

“…Following a solid/liquid separation process, the pregnant solution enters the precipitation stage, where carbon dioxide gas is bubbled to lower the pH of the solution and precipitate aluminum as aluminum trihydroxide [8][9][10]12,13]. Carbon dioxide is dissolved in the sodium aluminate solution according to Reactions (1) and ( 2) [12,[14][15][16]. With the increase in hydrogen ion concentration, resulting from the dissolution of CO 2 , the alkaline solution is gradually neutralized, reducing the pH and triggering the decomposition of the aluminate ion, resulting in the precipitation of aluminum hydroxide according to Reaction (3) [14][15][16].…”

“…Carbon dioxide is dissolved in the sodium aluminate solution according to Reactions (1) and ( 2) [12,[14][15][16]. With the increase in hydrogen ion concentration, resulting from the dissolution of CO 2 , the alkaline solution is gradually neutralized, reducing the pH and triggering the decomposition of the aluminate ion, resulting in the precipitation of aluminum hydroxide according to Reaction (3) [14][15][16].…”

“…Out of such aluminate solutions, alumina hydrates are precipitated by carbonation [21]. The carbonation process is carried out in temperatures of room temperature (RT) to 80 • C [14][15][16][22][23][24] and duration times ranging from 5-8 h [25]. Lee et al [26] showed that higher temperatures (70 • C) favor the formation of gibbsite, while lower temperatures (RT) favor the formation of bayerite.…”

“…Padilla et al [22] carried out the carbonation at RT, precipitating 97% of Al as boehmite and 20% of the silicon. Shayanfar and Aghazadeh et al [14][15][16] carried out extensive research on the carbonation of aluminate solutions resulting from the nepheline lime-sinter process. Both thermodynamically and experimentally, they have shown that at an ending pH of 9, 10 and 11, dawsonite, a mixture of dawsonite and imogolite and bayerite, correspondingly, are precipitated.…”

“…Apparently, the carbonation of sodium aluminate solutions is a process not sufficiently understood, as suggested by the literature review that was presented, concerning: the composition of the PLS undergoing precipitation is not always mentioned, temperature can range from RT to 90 • C, ending pH from 9.5 to 11, gas composition (% of CO 2 in gas), the gas flow rate, stirring, reactor design, the phases precipitating mentioned are not always the same, etc. [9][10][11][12][14][15][16][17][18][19]23,24,27]. The focus of the current work is to understand the effect of the concentration of unreacted sodium carbonate that remains from the leaching step and how it affects the type/composition of the precipitates and at the same time to maximize the recovery of aluminum in the form of alumina hydrates in synthetic sodium aluminate/sodium carbonate solutions.…”