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- The microscope photos clearly show deposits and encrustations. If necessary, a solubility test with HCl is carried out to differentiate between inorganic hydroxides and the like, and biological growth.
- Likewise, in the case of loose suspended substances, a backwash can be concluded as an improving measure. In the case of biological contamination, an additional disinfection might be necessary.
- Except for a few special types of exchangers, usable surfaces are very smooth, and macroporous beads are almost porcelain-like.
- Highly aged macroporous beads often show an initial transparency, which suggests the so-called gelation – a partial collapse of pores and thus a lack of accessibility.
- Anion exchangers in particular tend to absorb e.g. organic acids. This is easily identified by a considerable brown/red discoloration.
- However this is to be distinguished from the normal colour change between brown and light yellow, which occurs with gel anion exchangers between regenerated and loaded form.
- In the case of gel beads, internal cracking, which has not yet lead to fracture, can already be recognized. If this portion is higher than 5%, you must expect an increased fracture rate.
- At high portions of fractured beads, pressure loss or nozzle obstruction with channel forming in the resin bed are usual consequences.
- There is also the risk that cation exchange splinters get into the anion exchanger stage and there cause poor washout as well as increased conductivity, in particular during start-up. This effect depending on the extent of cation exchanger splinters often is irreversible and has to be detected in time.
- In the counting of the fracture components, often only relatively small numbers are given, e.g. 5…10%. These, hover, often signify a drastic limitation, since smaller fragments must be put together approximately into whole beads during the counting process. In the case of usually smaller fragments, the resin bed can thus be interspersed with splinters, which can have drastic consequences.
- The most commonly known characteristic is the volumetric total capacity, which can be found in the data sheet of the resins delivery form. Usually in addition to our measuring data we state the percentage loss relative to the new specification
- This capacity value, in conjunction with the volume-related capacity, provides information about the ageing state of the sample.
- Cation exchangers do not lose their groups, which can be seen in very consistent dry capacity values. If at the same time volume-related capacity decreases, weakening of the resin matrix by decrosslinking (with a volume increase resulting therefrom) must be concluded.
- In the case of anion exchangers, a reduction of the initial 4.5 and 5 eq/kg is observed over the years, which can reach as low as 3 eq/kg and lower. This decrease largely corresponds to the decrease in the volume-related TC and indicates that the resin structure (the resin matrix) hardly suffers, but the functional groups are released over time.
- One can set the following order of precedence from the sensitivity to ageing effects: Strong basic type 2 groups > strong basic type 1 groups >> weak basic groups. At the same time, type 2 groups become weak basic groups due to ageing. Type 1 groups are often completely lost.
- From the ratio of strong basic to weak basic groups quite a good measure of the extent of ageing can be derived.
The degree of quaternation, the proportion of the strong base to the sum of all basic groups, is introduced here.
- We have presented the way of interpretation, taking into account volume-related and weight-related capacity as well as spring water content, in a kind of decision tree.
- As an interpretation aid we have photographed and compiled stainings of new products as well as old samples in bad condition for some standard resin types. PDF files are available for download.
(PDF, 2.2 MB) Currently only available in German
– Interpretation aid –
(PDF, 2 MB) Currently only available in German
- In the column test breakthrough capacity, as well as the wash water requirement, is determined under normalized conditions at elevated speeds and limited regeneration agent usage.
- For the standard types of resin, we have determined reference values, which are valid as reference values. So you receive percentages that allow you the direct interpretation relative to new samples.
- Useable capacities of 95…100 % are good ≫ 85 % are significantly deteriorated. The reproducibility is about 3 %.
- The wash water requirement usually varies between 100 and 200 %, which then indicates a definitive problem.
- We have tested our methods for reproducibility through validation series. The measurement inaccuracies when repeating the TC measurement with the same samples can be found in the graphic:
- Systematic deviations are limited to < 1 % per component by carefully selecting the measuring devices and components.
- This allows you to interpret your capacity measurements to a degree of accuracy of 1…2 %.
- Weak basic fractions within strong basic types can only be specified with approx. 0.1 eq/l accuracy due to the often low absolute value.