IPCM n. 75 | May-June 2022

Page 78

INNOVATIONS: PRESENT&FUTURE

SPECIAL ISSUE ON ARCHITECTURE & DESIGN

Fluoride Removal with FLUORIDITE Edited by ALIT Technologies Srl San Bonifacio (VR) – Italy

M

info@alit-tech.com

any production fields have the technical need to use

A standard purification cycle, based mainly on an acidification phase

particular chemical formulations with high concentrations

(when necessary) followed by a neutralisation phase with lime, is very

of specific elements. For some specialised sectors in the

often not sufficient to achieve such low concentrations of fluorides,

surface treatment of steel, glass, and aluminium, for example, the use

even with considerable dwell times in the line.

of products with high fluoride concentrations is unavoidable.

In order to provide a truly effective solution to this problem without

Fluoride is the monoatomic anion of the fluorine atom. Due to their

necessarily having to intervene at the plant engineering level, ALIT has

high mordanting capacity and their affinity with metals (above all

developed FLUORIDITE, a liquid product that can be used directly on

aluminium and iron) and silica, its salts are key constituents of many

existing waste water treatment systems.

surface finishing products.

For example, in a three-tank purification line with a final sedimentation

However, there exist legal limits for the concentration of fluorides in

tank, a typical process involves adding FLUORIDITE in a concentration

surface and sewage water, which vary from country to country. For

of 500 to 3000 ppm in the first tank, where the acid and possibly

instance, in Italy, except for some stricter local regulations, the limit is

alkaline rinsing water and concentrates are conveyed. In the second

12 ppm for sewage and 6 ppm for shallow discharge.

tank, neutralisation with lime water to about pH 8 takes place. In the

In the specific sector of aluminium coating, however, the continuous

third and last tank, once the anionic polyelectrolyte has been added,

demand for higher productivity and pre-treatment quality has led to an

flocculation occurs.

increase in the use of chemicals, also resulting in critical issue in terms

The treated water then reaches the final sedimentation tank, where

of waste water management.

suspended sludge falls to the bottom and is then sent to the filter press

© ALIT Technologies

FLUORIDITE POLYELECTROLYTE

RINSE WATER

LIME/CHARCOAL

ALKALINE CONC. ACID CONC.

pH

pH

SEDIMENTATION TANK

DRAIN T3

T2

T1

FILTER PRESS Figure 1: Key elements of a standard purification process.

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N. 75 - MAY/JUNE 2022 - international PAINT&COATING magazine