*3.6. Regeneration Research*

In the regeneration process, the mp-CA/GOs that were individually loaded with Pb2+, Cu2+, and Cd2+ were immersed into 50 mL of 0.07 M HNO3 solution. Then, the mp-CA/GO was separated and washed sequentially with DI water, calcium hydroxide solution, and then DI water till the final eluent to neutral.

The recyclability of mp-CA/GO is depicted in Figure 11. The mp-CA/GO could remove Pb2+, Cu2+ and Cd2+ after 20 adsorption-desorption cycles with a performance loss within five %, possibly attributed to the GO, as reinforcing fillers, to maintain the mechanical strength and elasticity of mp-CA/GO during the continuous adsorption-desorption process.

**Figure 11.** Regeneration research of mp-CA/GO. (~ 50 mg of mp-CA/GO and 1.5 mM of Pb2+ solution were used here).
