MATERIALS HANDLING


specific to mining, including Genmine AS34, Genmine AS45 and Genmine AS26. Genmine AS26 was developed specifically for acidic minewaters and is particularly effective at inhibiting the formation of CaSO4


scale at low pH. A


series of threshold inhibiton jar tests were carried out under various conditions; altering the pH, Ca, SO4 and metal ion concentrations typical of those found in AMD waters. It was found that when other traditional antiscalants performed poorly at low pH, Genmine AS26 gave very good inhibition at high levels of saturation for CaSO4


(Figure 2).


FOULING OF MEMBRANES AND CLEANING Fouling can be described as the deposition of suspended solids within the feed water on the membrane surface and feed spacer. Te main sources of fouling in a traditional RO system are bacteria, clay, colloidal silica, organics and metal oxides/ hydroxides. Within mining the potential for fouling is even greater as the TDS values of feed waters; particularly iron, aluminium, manganese and sulphate ions are high. If correct pre-treatment is not used, the potential for fouling is further increased. Most traditional antiscalants are phosphonate and/or polycarboxylic based, which decrease in performance as the pH is lowered and therefore are largely ineffective against gypsum scaling in AMD waters.[6]


such as Genmine AS26 the CaSO4


By using an antiscalant should


stay in solution at low pH up until the limit of the chosen antiscalant’s capability. Changes in water chemistry that cause the saturation level to go beyond the capabilities of the pre-treatment is one of the primary reasons for the formation of CaSO4


scale within an RO system. If this


happens there will be a noticeable decline in permeate quality and membrane flux, as well as an increase in differential pressure across the membrane. At this point the membrane needs to be cleaned with the correct cleaner(s) in an attempt to remove the specific foulant and restore the permeate flux and salt rejection to previous values as well as improving the quality of the permeate. It is key that the onset of fouling is detected as early as possible as this will ensure that the membranes affected are recoverable. If a RO plant is poorly maintained and scaling and fouling are allowed to occur unabated, the cost of replacing the membranes in a


Figure 2. Graph showing the performance of Genmine AS26 against other traditional antiscalants at low pH.


big problem associated with AMD waters. In a mine with high levels of sulphate, the potential for scaling is even greater. Genesys International has developed some CaSO4


plant can be very expensive. In having a clean in place (CIP) protocol in place to ensure regular cleaning of the membranes the lifetime of the membranes can be extended. As already mentioned, CaSO4


effective at scale removal; called Genmine C15 and Genmine C17. Figure 1a shows the spacer filament


the microscope and Figure 1b presents the spacer filament after a three-hour clean with either Genmine C15 or C17.


in an RO membrane that is completely covered in CaSO4


CONCLUSIONS


AMD in mines has been an ongoing issue for the past number of decades. Trough the use of membrane technologies such as RO, this water can be treated for re-use on site, thus improving the environmental impact of a mine. Te main issue affecting this is the difficult water chemistries encountered in mining, such as low pH and high TDS values, resulting in rapid scaling and fouling of the membrane. Tis mini review has briefly highlighted how through good pre-treatment and the correct choice of antiscalant, the onset for scale formation can be decreased. Genmine AS26 has proven effective at preventing the formation of CaSO4


scale


at low pH and high TDS values. As well as pre-treatment this review has also


scale when viewed under


shown that CaSO4


scale can be cleaned scale is a


using newly formulated products Genmine C15 and Genmine C17 after only a few hours (three hours) of cleaning to restore performance within an RO plant.


specific cleaners that are very


References [1] Waterworld (2012) P. Szyplinska, “Thirsty world of mining: Harvesting new water solutions”– opened webpage 14/05/19.


[2] Mining Technology (2018) https://www. mining-technology.com/mining-safety/ samarco-dam-disaster-dealing-fallout- tragedy- opened webpage 14/05/19.


[3] The Conversation (2019) https:// theconversation.com/brumadinho-dam- collapse-mining-industry-needs-radical- change-to-avoid-future-disasters-112808 - opened webpage 14/05/19.


[4] A. Akcil, S. Koldas (2006) “Acid Mine Drainage (AMD): causes, treatment and case studies”, Journal of Cleaner Production, 14, 1139-1145.


[5] S.P. Chesters, P. Morton, M. Fazel (2016) “Membranes and Minewater – waste or revenue stream” IWWA.


[6] C Gabelich et al. (2004) Reverse Osmosis Pretreatment Challenges With Conventional Treatment AWWA Annual Conference & Exposition.


Gregory Gibson, Max Fazel and Stephen P. Chesters are with Genesys International. www.genesysro.com


www.engineerlive.com 45


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