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Precious metals finishing: the evaporation applied to water reuse and metals recovery

The customer
A precious metals refinery based in India, established a separate business line focused on metal-based products finishing for industrial customers. These products are targeted to improve conductivity and overall performance of the industries in which they are used, typically petrochemical, automotive, pharmaceutical, solar energy and electrical equipment in general.

Goals
Considering the large quantities of water used for finishing baths, their high pollutant level for the environment and the considerable quantity of precious raw materials dissolved in the exhausted baths, customer’s primary needs are certainly the recovery of metals as well as the water reuse in the production process to prepare fresh finishing baths or for any other purpose.

The solution provided
The EVALED solution we recommended to achieve these important goals has a double evaporation step. A first one to considerably reduce the initial volume of wastewater: two vacuum evaporators type EVALED RV F 15 made in superduplex stainless steel, having a distillate production capacity of 15 m3/day and a footprint of 8.2 m2 each.

A further and decisive reduction of wastewater volume is finally accomplished by the second evaporation step: two vacuum scraped evaporators type EVALED AC R in superduplex stainless steel, having respectively a distillate production capacity of 3 m3/day with a footprint of 6.6 m2 the first, and 6 m3/day and 9.9 m2 the second.

AC R is the series of hot/cold water evaporators/crystallizers with scraped heat exchanger
surface. The series is designed to treat wastewater containing a high concentration of suspended and dissolved solids and, for this reason, they are always the right choice when a second step of further concentration is needed.
If a thermal energy surplus is available on site, AC R evaporators are very cost-effective also from the OPEX side as they can work using cogeneration.

Repeat order
The plant has been finalized in two phases: the first installation included one unit of each type (RVF + ACR). After 9 years of efficient, effective and reliable operation, the initial units have been joined by two more units of the same type

Real results in terms of 

  • wastewater disposal costs reduction
  • low power consumption
  • water recovery

 are always the best proof.

The results:

  • Concentration yield 93.9%
  • Wastewater disposal cost reduction thanks to a concentration factor of over 16 times
  • Water reuse for manufacturing purposes
  • Precious metals recovery
Technology type Material Footprint (m2)
MVR Forced Circulation RV F 15 UNS S32750 2 x 8.2
Hot/cold water scraped AC R 3 UNS S32750 6.6
Hot/cold water scraped AC R 6 UNS S32750 9.9
Parameters U.M. Waste In Distillate Out Concentrate
pH 3.8-4 5 4-5
TS at 105°C % 3-10 <0.1 40-75
Conductivity μS/cm 48000 100-450
COD ppm 25000 300-2000
Nickel ppm 20-50 <5 200-1000
Copper ppm 15.5-30 <0.01 150-500