Discussion by Jacques J.P. BERNARD (France)
The application of reverse osmosis allows closed-loop operation with simultaneous re-utilization of
costly metals in the plating bath, and - production of high quality water recirculated at the inlet of
rinse tanks, which may eliminate or considerably reduce the quantity of make-up water.
The treatment of rinse water is always uneconomical, and reverse osmosis provides an almost
complete solution to waste water disposal problem in this type of industry. The process described by
Dr. GOLOMB for nickel should be applicable to other costly metals, which are the better retained by
semi-permeable membranes as they are of high molecular weights and valencies.
This study and these tests are to be compared to similar attempts made by means of ion exchangers
with recovery of metal salts and production of pure, or very slightly mineralized water which can be
recirculated. When ion exchangers are used, the reclaimed water is of a better quality but the regeneration effluent is of a composition somewhat different from that of the plating bath, thus making
some adjustments necessary.
But with reverse osmosis the concentrate has a composition very close to that of the plating bath.
However a drawback of this process seems to be the presence of salts, in particular toxic salts in the
permeate such as boric acid, and nickel which necessitates either a large dilution or additional treatment before disposal into a river.
It would appear that reverse osmosis allows higher concentrations than ion exchange in the
solution recirculated in the plating bath. However, some authors have reported that ion exchange gave
very close, and even higher values than those given by Dr. GOLOMB. We would like to hear of
practical experience on nickel or other metal recovery by ion exchangers, so as to better determine the
industrial interest of the process.
Reverse osmosis process economy relies on membranes life. The pressure exerted on the
membranes is the major element of their life and tests conducted under operating pressure are, in our
opinion, much more revealing than a mere contact of membranes in test solutions. But the tests by Dr.
GOLOMB seem to correspond to a rather short experiment. Test duration was limited to 3 months
with application of pressure about 8 hours a day, probably during working days only. It seems rather
optimistic to concludefrom a several hundred hours test that an 18 months' life can be expected from
membranes working on a continuous industrial basis, in particular with temperatures higher than
35 C, an important flow of boric acid and a recommended pH value of 4, all the more as the flow
through the membranes decreased by 30% during this test period. This reduction is attributed by the
author to an iron deposit and this has an evident influence; however, acid flushing finally gave only
50% of the initial flow in fact, could not this be caused by an important hydrolysis of membranes
made of cellulose acetate?
It is probable that the development of synthetic polymer membranes, which everybody expects,
will shortly enable us to achieve such chemical stability of the material that the problem raised by
hydrolysis will be eliminated, and permit the membranes to be cleaned more frequently and vigorously
without altering their performances.
A more realistic assumption on membrane life would be 9 months, and overdimensioning of the
unit appears necessary, to cope with flowrate decrease between two replacements. This overdimensioning may reach 50% with the corresponding influence on the quantity of membranes to
replace and material amortization.
The author admits an important difference in investment between a 500 gal/day and 5,000 gal/day
installation, expecting a noticeable difference due to scale. Modular building for reverse osmosis units
would show a quasi proportionality. In addition, the costs must include the price of waste water
treatment in a comparison of any process, with or without metal and/or water reclamation.
Are there industrial installations already operating according to the flow-sheet process proposed by
Dr. GOLOMB? If so we would be very interested to know the results and the main conclusions stating,
in particular the various advantages and disadvantages together with estimates of installation and
running costs.
579
The application of reverse osmosis allows closed-loop operation with simultaneous re-utilization of
costly metals in the plating bath, and - production of high quality water recirculated at the inlet of
rinse tanks, which may eliminate or considerably reduce the quantity of make-up water.
The treatment of rinse water is always uneconomical, and reverse osmosis provides an almost
complete solution to waste water disposal problem in this type of industry. The process described by
Dr. GOLOMB for nickel should be applicable to other costly metals, which are the better retained by
semi-permeable membranes as they are of high molecular weights and valencies.
This study and these tests are to be compared to similar attempts made by means of ion exchangers
with recovery of metal salts and production of pure, or very slightly mineralized water which can be
recirculated. When ion exchangers are used, the reclaimed water is of a better quality but the regeneration effluent is of a composition somewhat different from that of the plating bath, thus making
some adjustments necessary.
But with reverse osmosis the concentrate has a composition very close to that of the plating bath.
However a drawback of this process seems to be the presence of salts, in particular toxic salts in the
permeate such as boric acid, and nickel which necessitates either a large dilution or additional treatment before disposal into a river.
It would appear that reverse osmosis allows higher concentrations than ion exchange in the
solution recirculated in the plating bath. However, some authors have reported that ion exchange gave
very close, and even higher values than those given by Dr. GOLOMB. We would like to hear of
practical experience on nickel or other metal recovery by ion exchangers, so as to better determine the
industrial interest of the process.
Reverse osmosis process economy relies on membranes life. The pressure exerted on the
membranes is the major element of their life and tests conducted under operating pressure are, in our
opinion, much more revealing than a mere contact of membranes in test solutions. But the tests by Dr.
GOLOMB seem to correspond to a rather short experiment. Test duration was limited to 3 months
with application of pressure about 8 hours a day, probably during working days only. It seems rather
optimistic to concludefrom a several hundred hours test that an 18 months' life can be expected from
membranes working on a continuous industrial basis, in particular with temperatures higher than
35 C, an important flow of boric acid and a recommended pH value of 4, all the more as the flow
through the membranes decreased by 30% during this test period. This reduction is attributed by the
author to an iron deposit and this has an evident influence; however, acid flushing finally gave only
50% of the initial flow in fact, could not this be caused by an important hydrolysis of membranes
made of cellulose acetate?
It is probable that the development of synthetic polymer membranes, which everybody expects,
will shortly enable us to achieve such chemical stability of the material that the problem raised by
hydrolysis will be eliminated, and permit the membranes to be cleaned more frequently and vigorously
without altering their performances.
A more realistic assumption on membrane life would be 9 months, and overdimensioning of the
unit appears necessary, to cope with flowrate decrease between two replacements. This overdimensioning may reach 50% with the corresponding influence on the quantity of membranes to
replace and material amortization.
The author admits an important difference in investment between a 500 gal/day and 5,000 gal/day
installation, expecting a noticeable difference due to scale. Modular building for reverse osmosis units
would show a quasi proportionality. In addition, the costs must include the price of waste water
treatment in a comparison of any process, with or without metal and/or water reclamation.
Are there industrial installations already operating according to the flow-sheet process proposed by
Dr. GOLOMB? If so we would be very interested to know the results and the main conclusions stating,
in particular the various advantages and disadvantages together with estimates of installation and
running costs.
579