Water Treatment and Ion Exchange Test Work Capabilities

Multotec is the sole distributor of the Clean TeQ Continuous Ion Exchange technology in Africa. This novel continuous ion exchange technology is grounded in the basic principles of conventional ion exchange, with various key differences and associated benefits.

Conventionally ion exchange is implemented in the form of fixed bed batch ion exchange. Typically adsorption and desorption occurs here in one contactor and there is an absolute requirement here to have a clear solution with no suspended solids, as the presence of suspended solids reduces the performance of the system and makes it prone to blockages. The Clean TeQ technology however, departs from this convention and has the ability to effectively handle suspended and precipitated solids.

The Clean TeQ continuous ion exchange process is governed by two main principles:

  • Continuous movement of ion exchange resin and solution; and
  • Counter current movement of ion exchange resin and solution

The continuous movement of ion exchange resin allows for operation of both adsorption and desorption closer to ideal equilibrium conditions. The efficiency of the adsorption process depends primarily on the number of theoretical adsorption stages in the adsorption column and the transfer kinetics of the ion exchange resin. When operating the process continuously, discrete amounts of loaded resin are removed and fresh resin added on a continuous basis. This allows maximum recovery of target species and a high degree of process efficiency to be achieved. The resin movement also allows for increased solids handling capabilities, with the risk of resin bed fouling significantly decreased. The counter current movement of resin and solution also promotes the formation of a concentration gradient within the resin bed, further improving ion exchange efficiency.

In order to support this technology Multotec has set up a laboratory and developed piloting test work capabilities.

Laboratory Capabilities

Multotec has set up a fully equipped laboratory that is capable of handling all the necessary upfront test work required to assess a specific water source for treatment with the Clean TeQ technology. The laboratory is used to conduct ion exchange test procedures such as initial resin screening, ion exchange equilibrium test work and bench-scale column loading and adsorption to determine kinetics.

Initial resin screening is a process during which different resins are tested to determine the best resin for the application.

Equilibrium isotherm testing is a key first step towards the design of an ion exchange system. A bottle roller is used to contact resins with the feed solution at varying resin-to-solution ratios for a 24 hour contact period. The results of this test are then used to determine the equilibrium loading capacity of the resin for a specific feed composition. These results are used to either set up the lab-scale piloting or to ultimately design the ion exchange system for the specific application.

Multotec’s water treatment laboratory also has the capabilities to mimic and test various upfront pre-treatment steps, such as neutralisation and precipitation via bench-scale beaker precipitation tests. Multotec can also perform filtration tests on the sludge produced in these tests using its solid-liquid separation test work capabilities.

The laboratory also performs batch resin desorption tests, whereby resins are contacted with various desorption reagents in order to confirm the optimum desorption reagent for a specific application.

Laboratory Scale Piloting

Multotec’s water treatment laboratory is equipped with two lab-scale continuous ion exchange pilot units which operate at a typical flowrate of 6 L/h. Multotec has the flexibility to operate these units either on a customer’s site or at Multotec’s premises, depending on customer requirements.

Typical objectives of lab-scale piloting include:

  • Determine the optimum resin ratio
  • Determine the maximum water recovery achievable at this optimum resin ratio
  • Determine optimum pH to initiate a resin transfer
  • Confirm loading efficiency achieved using continuous counter current movement of the ion exchange resin.
  • Determine the waste/brine composition

The pilot setup simulates the continuous and counter-current movement of resin and operates as a lab-scale replica of the full-scale plant, thereby accurately simulating full-scale operating conditions.

For lab-scale piloting Multotec’s laboratory also has the capabilities to carry out bulk precipitation or neutralisation, thereby simulating any pre-treatment conditions.

During the lab-scale pilot, pH and electrical conductivity is typically monitored and logged on a continuous basis, with a third party laboratory conducting detailed analytical tests on samples taken on a regular basis.

Continuous Ion Exchange Test rig

In addition to the laboratory, Multotec has invested in a 1 m3/h test rig. The rig was originally used as a demonstration unit at Electra mining Africa in September 2014. Since then, the rig has been modified to be used as a fully functioning pilot unit and has been installed at the Multotec premises. The test rig can be used to conduct  pilot scale test work for customers on their sites. The rig is a dual stage continuous ion exchange system. It consists of two stages in series, one to remove the cations such as calcium and magnesium and one to remove the anions such as nitrates and sulphates. The two stages are set up to operate independently and can therefore be utilised to do single stage test work as well. The rig is fully automated and operates with minimal operator intervention. The test rig can be utilised to do long-term evaluations of the operational performance of the technology.

Sample requirements

Sample requirements are dependent on the feed solution and the test work to be conducted.

Typical requirements are as follows:

  • Initial testwork – Equilibrium loading isotherms: 20 L of feed solution
  • Lab-scale piloting – 300 to 500 L of feed solution.

Recent Test work Case Study

Multotec’s laboratory recently completed test work that investigated the treatment of cooling tower blowdown, as well as reverse osmosis reject water from a coal-fired power station. This work investigated the treatment of these waters using Multotec’s novel dual stage continuous ion exchange system, called DeSAlx®. The viability of removing calcium, magnesium, sulphates and chlorides from the cooling tower blowdown and reject water was evaluated.  The proposed system consists of a set of ion-exchange resins combining cationic and anionic exchange stages. For this study, removal of calcium and magnesium was evaluated using a strong acid cation resin. A weak base anion resin was used for sulphates and chlorides removal.

Experimental work was conducted in two phases. The first phase involved ion exchange equilibrium isotherms to establish the optimum resin-to-solution ration. Thereafter, pilot work was conducted using a lab-scale continuous counter current ion exchange setup in the form of two columns in series filled with approximately 2 L of strong acid cation and weak base anion resin respectively. The pilot unit simulates the counter current movement of the resin and solution. The loaded resin was contacted with dilute sulphuric acid to regenerate the cation resin and a hydrated lime solution to regenerate the anion resin.

During the isotherm studies (laboratory experiments), it was established that an optimum operational resin-to-solution ratio of 1:50 would be used for further testing. The results of the pilot work showed that for the blowdown water, 99.8 % removal of calcium (Ca2+) and 98.9 % removal of sulphate (SO42-) was achieved during steady state operation. For the reverse osmosis concentrate a 99.8% removal of Ca2+ and 99.7% removal of SO42- was achieved. During steady state, the average turbidity in the final product water was 1.47 NTU. This showed a consistent removal of suspended solids, whilst still achieving effective removal of the dissolved elements. No upfront filtration was required on either of the wastewaters tested.

 

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