298 94 307/02 Untersuchungen zum Stand der Umsetzung des ...

Teil 3 Seite 6-14
For 1000 kg of degreased bone, containing 8 % water and having 63 % comprising 7 %
CaCO3 and 56 % Ca3(PO4)2, approximately 7700 litres of 4 % HCl is required, for com-
plete conversion.
The solid “ossein” residue is used in the gelatine manufacture process. This process
may take several days depending on the nature, size and density of the raw material.
Several pits, e.g., six, sit in series, containing ossein, at various stages in the process.
Fresh acid with a concentration of 3.5 % hydrochloric acid, is added to the pit containing
the ossein which has been treated for longest, after about one day this acid is pumped to
the pit containing the second oldest ossein, whilst the acid from this is pumped to the pit
containing the third oldest ossein. The process continues by this batch counter-current
action. In this way the “newest” liquor, with the highest acid concentration and lowest
concentration of monocalcium salt is extracting the salt from the ossein with the lowest
available yield and the “oldest” liquor, with the lowest acid concentration, i.e., about 0.5 %,
is extracting the salt from the ossein which has most salt to give up. The process can be
helped by air agitation. The process is illustrated in Figure 6.1
Each reactor tank in the process may typically contain a batch of 20 – 50 tonnes of bone
chips, but smaller tanks may be used. The tank height may be about 7 metres and the
diameter about 3.5 metres. New reactors are usually made from plastic coated steel. For
a system with 4 reactor vessels of which every day one reactor is emptied and one is
filled, 200 tonnes of degreased bone chips can be treated in four days, in 4 batches of
50 tonnes. To demineralise these approximately 1540000 litres of 4 % hydrochloric acid
is required. When the efficiency of the process is approximately 90 %, this becomes ap-
proximately 1710000 litres in four days or about 17800 litres/hour.