**2. Material and methods**

#### **2.1 Apparatus**

The CE 300 Ion exchange demonstration unit (Gunt Hamburg, Germany) is used in this work. The apparatus facilitates tests relating to water softening and demineralization; it is equipped with both cation and anion exchangers with strong and weak basic or acidic contents. The unit layout is illustrated in **Figure 2**. CE 300 enables water deionization with the aid of cation and anion exchangers. The raw water is pumped from the tank into the top of the cation exchanger. In the softening process the water flows from there back into the collecting tank. To desalinate the raw water, it is then additionally routed through the anion exchanger. From there the treated water passes into the collecting tank. In the regeneration process, acid or caustic is fed into the ion exchangers from below using the same pump. The acid and caustic used is collected in the collecting tank. The flow rate of the pump is adjustable, and can be read from a flow meter before it enters the first ion exchanger. For continuous evaluation of the process, a conductivity sensor is installed upstream of the inlet into the collecting tank. The measured values can be read from a conductivity meter. Samples can be taken at all relevant points. Tap water can be used as raw water.

Commercial cation and anion exchangers were provided by Gunt Hamburg (Germany). The strong acidic cation polymeric exchanger resin is commercially called

#### **Figure 2.**

*CE300 unit diagram: Flow path with the two ion exchangers configured in series (desalination): 1 collecting tank, 2 anion exchanger, 3 cation exchanger, 4 pump, 5 raw water tank; E conductivity, F flow rate.*

MERCK 104765 cation exchanger IV with capacity greater than 3.2 mmol/ml; while the strong basic anion polymeric exchanger resin is commercially called MERCK 104767 anion exchanger III with capacities greater than 1.0 mmol/ml.

#### **2.2 Methodology**

The set-up was prepared by opening/closing valves as described. Solutions of 5 vol% of HCl and 0.1 vol% of NaOH each in 100 mL distilled water were prepared. The cation tube was filled with the 5% HCl solution and the anion tube with the 0.1% NaOH solution; each containing 20 g polymeric resin. The process started by pumping the hard water through the column, and water was allowed to pass through the outlet tubes. Once a steady flow is passing through the outlet, the conductivity of the water at the outlet was recorded at time intervals of 10 seconds. The pump turned off when the conductivity values start to increase until reaching a steady state. The experiment was repeated with other concentrations of HCl and NaOH with 0.5 and 0.1 increments, respectively.

For the purpose of studying the effect of amount of water treated, the process was repeated at certain concentrations of HCl and NaOH with the tubes filled with different amounts of hard water. Also, the effect of amount of resin used was studied by pacing different amounts of resin at the different runs for given concentrations of HCl and NaOH.

#### **3. Results and discussion**

#### **3.1 Effects of acid and base concentrations on deionazation**

Resin generation is important from cost point of view as well as minimizing solid waste. In this work, resin regeneration using different combinations of acid in the cationic resin and base in the anionic resin, each at different concentrations, was accomplished. Each bed was fed with 20 g of polymeric resin and each filled

#### *A Comprehensive Method of Ion Exchange Resins Regeneration and Its Optimization for Water… DOI: http://dx.doi.org/10.5772/intechopen.93429*

with 2 L of hard water. The hard water is municipality tab water with a hardness conductivity of 100,000 μS and a TDS of 600 mg/L. The experiment was started off by putting 0.5 vol% HCl and 0.1 vol% NaOH in the cathodic and anodic resin tubes, respectively; and in every different run the vol% was increased by 0.5 and 0.1 for each of the aforementioned resins. The results for water conductivity at different combinations of acid-base are shown in **Figure 2**, having in mind that the conductivity of purely deionized water is 1.1 micro Siemens (μS).

The experiment was started off by using 1-vol% NaOH and 5-vol% HCl in the cathodic and anodic resin tubes, respectively. It is seen (**Figure 3**) that conductivity starts to decrease indicating that the resin is deionizing the water until a point is reached where the conductivity starts to increase again, indicating that the resins have reached accumulation point. Accumulation point was reached after 5 seconds of running the experiment, and the maximum value of regeneration was found to be 1550 μS. When 0.9 vol% and 4.5 vol% of NaOH and HCl, respectively, were used the conductivity kept decreasing until a value of 1076 μS was reached in 45 seconds. The same trend was noticed when the NaOH and HCl vol% were decreased to 0.8 and 4% respectively; however, in this run a higher conductivity of 2270 was obtained in 45 seconds. This shows that as the amount of resin decreases, the conductivity of water increases indicating that fewer ions were removed. In **Figure 3**, a conductivity of 2140 μS was obtained at 45 seconds, when 0.9 and 4.5% NaOH and HCl, respectively, are used. More time was required to deionize the water for the case of 0.9 and 4.5% NaOH and HCl, respectively; at 45 seconds the conductivity was found to be 2360 μS. Furthermore, the conductivity was found to be 2260 μS at 45 seconds for the case 0.6 and 3.0% NaOH and HCl, respectively. Furthermore,

as the vol% decreased, the conductivity started giving similar results at 45 seconds. For example, for the cases of 0.3% NaOH—1.5% HCl, 0.2% NaOH—1.0% HCl, and 0.1% NaOH—0.5% HCl, the conductivity was found to be 2300, 2100, and 1867 μS, respectively, which are close to each other. In conclusion, to have best results, the resin vol% should be high.

#### **3.2 Effect of treated volume on deionization**

Effect of treated voume of water was also investigated using same amount of resins in each bed (20 g) and same eluants concentrations in the cationic and anionic resins (5 vol% HCl and and 1 vol% NaOH, respectively). The results for water conductivity at different amounts of treated water are shown in **Figure 4**. As shown in **Figure 3** for the case of 1 L, the conductivity started to decrease indicating that the resins are deionizing the passing water. It started off with a conductivity of 864 μS which is the conductivity of tap water and ended with a conductivity of 73.19 μS. When the volume increased to 2 L, the lowest conductivity was found to be 70 μS after 140 seconds have passed. On the other hand, when 3 L of water was added, 1.14 L of water was treated and the lowest conductivity was found to be around 77.2 μS; after this point, the conductivity increased again and that happened at 70 seconds (**Figure 4**). For the case of 4 L of water being added, an amount of 1.63 L of water was treated. The lowest conductivity was found to be 242 μS and then it started to increase at 70 seconds. This shows that as more water is being treated, the conductivity increases.

### **3.3 Effect of amount of resin**

The effect of amount of resin used in cationic anionic resin tubes on deionixation is also studied by putting different amounts of resins in each tube with

*A Comprehensive Method of Ion Exchange Resins Regeneration and Its Optimization for Water… DOI: http://dx.doi.org/10.5772/intechopen.93429*

**Figure 5.**

*Effect amount of resins on resin regeneration using 5-vol% HCl in cationic resin tube and 1-vol% NaOH in anionic resin tube.*

different volumes of hard water as 3 using 5 vol% HCl in the cationic resin tube and 1 vol% NaOH in anionic resin tube. The results are shown in **Figure 5**. The case of 20 g resin is the same as the described in the previous section. When the amount of resin was increased to 40 g, the same trend was obtained as that of the 20 g resin. However, more water was deionized in this case because more resin was used. In other words, it required around 480 seconds to saturate the resin and to stop the deionization process. This shows that increasing the resin amount, helps in increasing the deionization efficiency. The resin amount was again increased to 60 g. The water was being deionized until 560 seconds were reached and a conductivity of 19.8 μS was obtained. After this point, the conductivity started to increase again indicating that the resin has been saturated. As the resin amount increased, the apparatus was able to give better results in terms of removing more ions from the water. For example, at 500 seconds the conductivity was found to be 38.6 and 20.4 μS for the 40 and 60 g, respectively. This shows that the amount of resin is related to the deionization efficiency. As the amount of resin increases, more ions are removed.

#### **4. Conclusions**

Water conductivity decreases with the increase in resins concentrations; the lowest conductivity is achieved when using 1-vol% NaOH and 5-vol% HCl in the cathodic and anodic resin tubes, respectively. The results of this work show that water conductivity increases with the increase in the amount of water being used. The amount of resin significantly impacts the deionization efficiency; more ions are removed as the amount of resin increases. The optimization implemented in this

work is considered superior compared to other deionization techniques due to life time and efficiency of the reused resins.
