**5.1 Adsorption of heavy metals**

The general sources of heavy metals are weathering of rocks due to their abundance in nature and mining industries as a result of mineral process of metal ores [61]. Various heavy metals known to pollute water include nickel, cadmium, lead, mercury, chromium, arsenic and copper. The water pollution by these toxic metals is a global concern owing to their acute toxicity and enduring accumulation [67].

Heavy metals are problematic since they are mutagenic, carcinogenic, are not biodegradable and can form various species [68].
