True-Size Column Tests - Low Flow Rate (110 to 150 ml/min)

The results for MetaWool in a MIX2000P column are shown in Figure 1. The variables in this test were as follows:

Figure 1 shows that the silver concentration in the effluent was below 1 ppm for most of the life of the column, with a very sharp increase at the end. This means that Metafix MRCs can easily and consistently meet the silver discharge limits imposed by almost any municipality.

The breakthrough point occurred somewhere between 2,300 and 2,334 liters (approximately 600 gallons). This volume was due to the relatively high influent silver concentration (average of 2,700 ppm). At breakthrough, the Metafix MIX2000P MRC recovered 6,301 grams or 6.3 kg of silver.

Figure 1: Performance of a Metafix MiX 2000P MRC

Volume of silver-rich solution desilvered in liters

Metafix MRCs can also be configured in parallel to increase throughput. The results of a field test using two MIX2000P cartridges in parallel are shown in Figure 2. The variables in this test were as follows:

Figure 2 shows the remarkable consistency and efficiency of Metafix MRCs. The effluent silver concentration from each of the two cartridges was virtually identical, varying on average by only 0.0125 ppm. For the entire 3,394 liter test (700 gallons), the average effluent silver concentration was 0.57 ppm. This would easily meet the silver limit in most municipalities. In addition, each of the two MRCs recovered 7.7 kg of silver.

The cartridges performed better in this field test than in controlled laboratory tests. This may have been due to less variability in both influent silver concentration and pH. Since this was a field test, the MRCs were changed prior to breakthrough in order to avoid exceeding 5 ppm of silver.

Figure 2: Performance of two Metafix MiX 2000P MRCs running in parallel

Comparing a Low Flow Rate Metafix MRC With a Competitor's MRC

A competitor's MRC was tested against a Metafix MIX2000P column. The medium in the competitor’s MRC comprised iron sprayed on a fiber support. There was approximately the same weight of iron in the Metafix MRC as in the competitor’s MRC. The performance results of this comparison testing are shown in Figure 3. The variables in this test were as follows:

Figure 3 shows that the Metafix MRC recovered more than twice the weight of silver, while maintaining a lower effluent silver concentration. There was also much less variability in effluent silver concentration in the Metafix MRC.

Figure 3: Comparison test: Metafix MiX 2000P MRC vs. competitor's MRC

Volume of silver-rich solution desilvered in liters

True-Size Column Tests - High to Very High Flow Rates (1 to 12 L/min)

The normal flow rate of solutions passing through commercial MRCs ranges from 30 ml/min to 150 ml/min. Significantly higher flow rates were tested with Metafix MRCs.

Figure 4 shows the results of testing with high flow rates through a Metafix MIX5000 cartridge. The variables in this test were as follows:

A flow rate of 1 L/min was significantly higher than the norm for MRCs. With the Metafix MIX5000, even at this relatively high flow rate, the effluent silver level remained below 5 ppm until after the cartridge had recovered almost 15 kg of silver.

With floor space at a premium in most facilities, higher flow rates translate into fewer storage requirements. For wholesale and professional photofinishers, the MIX5000 columns offer another key advantage; they can be used for primary and secondary silver recovery, thus eliminating the need for electrolytic silver recovery. The columns require little maintenance, significantly less electricity, and no pH and sulfite adjustments.

Figure 4: Performance of a Metafix MiX 5000 column (flow rate = 1L/min)

Volume of silver-rich solution desilvered in liters

Figure 5 shows the results of testing the largest Metafix MRC -- the Oliver -- using a very high flow rate of 12 L/min. The variables in this test were as follows:

After desilvering 5,500 liters (1,400 gallons) of solution, the effluent silver concentration was still less than 5 ppm. The Oliver recovered more than 12 kg of silver. For desilvering large batches of solution, the Olivers are a cost-effective alternative to high-amperage electrolytic silver recovery.

Figure 4: Performance of a Metafix

Volume of silver-rich solution desilvered in liters