Abstract
Aluminium exerts undeniable human health effects, so its concentration should be controlled in water treatment plants. The article presents and discusses the results of studies on the influence of selected properties of aluminium coagulants on the concentration of aluminium remaining in the purified water. The coagulants used were classical hydrolysing aluminium salts: aluminium sulphate (VI) and sodium aluminate as well as pre-hydrolysed polyaluminium chlorides: Flokor 105B and PAX XL10 that had different the alkalinity coefficient r = [OH−]/[Al3+]. The Al species distribution in the coagulants samples were analysed by the Ferron complexation timed spectrophotometry. On the basis of their reaction rates with ferron reagent, the aluminium species were divided into three categories: monomeric (Ala), medium polymerised (Alb) and colloidal (Alc). The usefulness of the tested aluminium coagulants due to the concentration of residual aluminium and dissolved aluminium, which is easily assimilated by the human body, was increased according to the following series: sodium aluminate (Ala = 100%, Alb = 0) < aluminium sulphate (VI) (Ala = 91%, Alb = 9%) < PAX XL 10 (Ala = 6%, Alb = 28%, r = 2.10) < Flokor 105B (Ala = 3%, Alb = 54%, r = 2.55).
Highlights
Aluminium is found in all natural waters and waterworks
The chemical species of hydrolysed Al(III) can be divided into three types according to their reaction kinetics: monomeric Al species (Ala ), medium-polymerized Al species (Alb ) and species of colloidal (Alc )
Because of the concentration of aluminium remaining in the purified water and the share of aluminium dissolved in the remaining aluminium, which is best absorbed by the human body, the usefulness of the studied aluminium coagulants was increased with an increase in the content of polycationic aluminium forms (Alb ) and with an decrease in the content of monomeric aluminium forms (Ala ) in the coagulants tested
Summary
Aluminium is found in all natural waters and waterworks. It may occur in the form of organic and inorganic compounds in dissolved and undissolved form, and an important factor that affects its form of occurrence is the pH value [1,2]. It is amphoteric, combining with both acid and bases to form, respectively, aluminium salts and aluminates. The chemical nature of aluminium in water is essentially the chemistry of Al(OH) that has an amphoteric character and tendency to form complex ions and polymerise.
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