Which variant of the Zadra process are you using? Pressure/atmospheric/solvent-assisted? What is your eluant mix?

Probably all of the above will have an impact, and then add temperature>115C, pressure, water quality (ionic strength - lower is better), E/W single pass efficiency for starters. With your ore, presence of copper, arsenic and antimony may have an influence.

I gather it is a pressure Zadra elution, in which case your column temperature needs to get above 115C or rate will very slow. Water quality is very critical for AARL elution, not so much for Zadra, but you should still use the best quality available for eluant make-up. Not process water. E/W single pass efficiency is critical for Zadra because gold not recovered is then re-circulated back to the elution column, slowing down the elution rate. Eluant flowrate is not too critical in the 2-4 BV/h range. You should be achieving optimum elution with about 30 BV of eluant through the column (15h at 2BV/h). Eluant mix of about 2% caustic and <1% cyanide is typical.

I am currently sampling the eluant, eluate, loaded and eluted carbon the idea is to look at gold analysis and composition of both solution samples. Is this the right way of evaluating electrowinning efficiency? I think single pass efficiency is poor maybe due to presence of base metals.

I am currently sampling the eluant, eluate, loaded and eluted carbon the idea is to look at gold analysis and composition of both solution samples. Is this the right way of evaluating electrowinning efficiency? I think single pass efficiency is poor maybe due to presence of base metals.

All things considered my take would be you decide what cut off is acceptable for you. If your gold balance overall dictates that you do a 4 or 6 or 12 ton elution per day, then your elution should be done in the same day to maintain the inventory balance- in a Zadra system 18-20 hrs recycle is not uncommon even honouring all metallurgical parameters- it also depends on the cell activity, frame quantity, power draw, water quality etc. monitor the column outlet tenour to the electrowinning cell and if that flattens you should consider wrapping up.

If you have base metals like copper on the carbon, they can be removed after the acid washing stage already before elution to increase the gold recovery and lower the base metal content of the bar.

The electrowinning efficiency is between the inlet and outlet of the cell(s) itself as an operating unit- you cannot penalize/criticize the electrowinning cell efficiency if you have the correct voltage/amps/cathodes and design flow- I suggest you do a series of 5 minute sampling on the column outlet, cell outlet and look at the isotherms- if the cells are a issue the outlet grade will be high for a long period, if the elution is slow the outlet grade from the column will stay high for a long period- then match the performance line for a couple of elutions and draw conclusion from that.

Of course if the loadings on the carbon increase for some reason more than design, it will result in inefficiencies downstream.

Some queries/comments:

1. May I assume this is a Zadra pressure strip (up-to 290 F & 70 PSIG);
2. Strip time (generally a whole shift or 12+ hr);
3. NaCN/NaOH? target 1-wt%/0.1-wt%;
4. What is your BV/hr...target ~2.5;
5. Is your LC H+ washed & tramp items screened?
6. Are you bleeding strip solution inventory to minimize build-up of impurities & replenishing w/fresh strip?
7. Coarse & fine C screen checks?
8. LC & SC Ca+2 levels?

Has the removal or prevention of scale been practiced on the circuit? The inlet screens to the strip vessel are one location for scale formation due to the pressure drop. The heat exchangers are another location due to temperature and pressure drop. Have these two locations been checked? Flow restriction due to scale will reduce the amount of heat that can be transferred to the elution process.