Ageing of aluminium hydroxide flocs

Cellulose‐Based Biotemplated Silica Structuring

“…[36] Considering the fraction of alumina polymorphs found in the earth's crust (16 mass%) and in biominerals (nil), it is apparent that other factors are of importance. This also causes its low solubility in water (and therefore low actual availability), [38] high polarity of the dissolved molecule, high tendency of hydrolyzed species to condense in water [39] and a crystal growth with sizes rapidly exceeding the intricate nanometer structuring of the natural scaffold. This also causes its low solubility in water (and therefore low actual availability), [38] high polarity of the dissolved molecule, high tendency of hydrolyzed species to condense in water [39] and a crystal growth with sizes rapidly exceeding the intricate nanometer structuring of the natural scaffold.…”

“…The main one is that, since all reactions carried out in nature are enzyme catalyzed and with low enthalpy changes, [37] the low negative (and therefore high absolute) standard enthalpy of formation of crystalline alumina makes it an unsuitable candidate, despite its apparent occurrence. This also causes its low solubility in water (and therefore low actual availability), [38] high polarity of the dissolved molecule, high tendency of hydrolyzed species to condense in water [39] and a crystal growth with sizes rapidly exceeding the intricate nanometer structuring of the natural scaffold. Silica, on the other hand, is characterized by a condensation behavior where the different degrees of polymerization are in close equilibrium to each other.…”

Élimination des phosphates par filtration directe sur lit de sable

“…Les conditions d'agitation jouent un rôle très important dans le processus de floculation (MlYANAMI ef al., 1982 ;FRANÇOIS, 1987 ;ELMALEH et JABBOURl, 1991 ;CHEN et al, 1997), c'est la raison pour laquelle différentes valeurs de G ont été testées en fixant Al/P = 2 (figure 7). On observe que pour la valeur de G = 50 s -1 , les concentrations résiduelles en phosphore sont inférieures à 0,25 mg/l.…”

Coagulação/floculação de suspensões ricas em óxidos de ferro por sulfato de alumínio

“…Como coagulante empregou-se uma solução estoque (1% p/v) de sulfato de alumínio P.A. Al 2 (SO4) 3 (14 a 18 H 2 O -marca Cinética), preparada com antecedência de 24 h em relação ao momento de sua utilização, visando uniformizar eventuais efeitos de "envelhecimento" do sal de alumínio sobre seu efeito coagulante 13 . Os ensaios de coagulação/floculação seguiram o procedimento tradicional de "JarTest" (Jar-Test Milan, modelo JT 101), com 6 jarros, agitação rápida de 120 rpm durante 2 min, seguida de etapa lenta com velocidade de 20 rpm durante 20 min e tempo de sedimentação de 2 h. Foram adicionadas dosagens crescentes de sulfato de alumínio a volumes de 500 mL de suspensão contidos nos jarros, em diferentes condições de pH inicial.…”