switches. This should be done periodically so that the  extractant phase surge tank volume can be adjusted as  needed to maintain sufficient extractant phase volume to  provide steady operation over extended periods, for example  weeks, months and possibly years. The stirrers for the  mixers were then powered up, adjusted and maintained at  steady-state by the following procedures.  All of the mixers were set between 700-1700 rotations per  minute (rpm). The mixers needed at least 15 minutes to  warm up, preferably 30 minutes. During this time the mixers  were monitored and adjusted, usually decreasing the rotation  rate in order to avoid excessive mixing. Excessive mixing is  very undesirable; it can lead to problems such as spatter as  well as the formation of fine emulsions that require longer  phase coalescence time in the settlers. Although any type of  stirring is sufficient enough to mix medium to low viscosity  immiscible fluids, disk or fin type stirrer pumps are pre› ferred. They are both designed to pull the two fluids,  aqueous and extractant phase, into the mixing compartment  from the upstream mixer settlers. The shearing blades of the  mixers generate micro droplets that create a very high  interfacial surface area that is critical to fast contaminant  extraction and strip kinetics. Higher mixing speeds accom› modate shorter residence time of the fluid in the mixer and  compensate for extractant/aqueous ratios other than 1: 1.  Although stirrer speeds that result in the mutual blending of  only 20% of the two phases is sufficient, a blend of at least  80% is preferred and if optimum conditions can be achieved  95-100%. Excessive mixing is suitable but less preferred if  the resultant emulsion formed requires mixing for long  periods of time to disengage and break due to exceedingly  fine droplet size. Mixing conditions preferred by the inven› tion is about 12-120 seconds, preferably 30-90 seconds, and  optimally 45-seconds. The total hydraulic fluid residence  time in the apparatus will be the sum total of the volumes of  the individual operations of the apparatus, including mixers,  settlers, pumps and surge capacity. Due to the low values  and/or quantities of the contaminants present in the Acid  Mine Drainage water purification process (Fe, Al, Se, Si,  Mn, Zn, Ni, Co, Ca, SO$_{4 }$ - 2 ), and the very high flow rates of  10-10,000 gal/min (averaging about 500 gal/min, but often  variable) of water, conventional metals extraction by LLX is  not feasible because of the very large equipment and E/A  ratio requirements that would be required for the large  aqueous flows involved in water purification. Although the  mixing conditions can be either extractant phase continuous  or aqueous continuous, the latter is the more typical since  special startup conditions are not needed to achieve it.  After this initial loading of strip solutions and the warm  up time for the mixers are both complete, the system was  now ready for the charging of the Acid Mine Drainage feed  water and (the acid mine drainage feed pump was set to 145  ml/min at system start-up) the extractant phase feed streams.  The N-extractant (extraction circuit designed to extract +2  metal ions) feed flow rate at system start-up was set to 28  ml/min, and the M-extractant (extraction circuit designed to  extract +3 metal ions) feed flow was set at 7.3 ml/min. The  extractant surge tank for this process was a 6 L clear  chemical resistant PVC tank. Other feed agents are listed in  the LLX Test Condition Key in Table 5.  TABLE 5  US 10,494,270 B2  64  63  AMD  Flow  Run  Rate  #  mL/min  100  100  4  100  5.1  100  LLX Test Condition Key  ( extractant phase test conditions with extractant formulation selection for each test trial.)  LLX Test Condition Key  Extractant  Extractant  Flow Rate  Flow Rate  (N Circuit)  (M Circuit) E/A  mL/min  mL/min  Ratio  17  8  1/6  17  1/6  20  1/5  20  1/5  Mixing  Residence  Time  Extractant  second  Formulation  333.6 (640 mL Aliquat 134: 15%  mixer- IDA: 15%  settler)  Calumet: 70%  333.6 (640 mL Aliquat 134: 15%  mixer› settler)  IDA: 15%  Calumet: 70%  307.2 (640 mL Aliquat 134: 15%  mixer› settler)  IDA: 15%  Calumet: 70%  90 (180 mL  Aliquat 134: 15%  mixer› settler)  IDA: 15%  Calumet: 70%  Test  Objective  Basic LLX  process  evaluation  and key  parameter  range  finding  LLX process  evaluation  LLX process  evaluation  and  Determining  15%  Na2C03  consumption  rate  LLX process  evaluation  and  Determining  15%  Na2C03  consumption  rate  Process  Configuration  Note  Scheme 1  Scheme 1  Added  ceramic  milling rods  in  0/W  separator  Scheme 1  Added  ceramic  milling rods  in  0/W  separator;  Used sep.  funnels as  decanters  Scheme 1  Added air  floatation  device and  ceramic  milling rods  in  0/W  separator 