Adsorptive removal of heavy metals from wastewater using brick waste and copper smelter slag as low cost adsorbents

The industrial effluents contain substantial amounts of toxic heavy metal ions which pollutes

surface water and groundwater. In this study, the adsorptive removal of copper, iron and

nickel ions from wastewater using Makoro Granite brick waste (MGBW), Makoro Gold Satin

(MGS) clay brick waste, copper smelter slag (CSS) and cement brick waste (CBW) as novel

adsorbents has been investigated at batch mode. The mineralogical and chemical content of

adsorbents was determined using X-ray Diffractometer (XRD) and X-ray Fluorescence

(XRF) respectively. Thermogravimetric analysis (TGA) on both adsorbents prior to and after

adsorption was done. Surface morphology of media and pH point of zero charge (pH pzc)

were respectively investigated and determined using Scanning Electron Microscopy (SEM)

and pH drift method. The leaching behaviour of media was investigated at different contact

times; 24, 48 and 72 hours. The batch investigations focused on the effects of contact time,

pH of solution, adsorbent dosage or loading, temperature, and adsorbent size to determine the

effectiveness of the media. XRD revealed amorphous and crystalline phases on both media

without noticeable changes before and after adsorption. The pH pzc of CBW, MGBW, MGS

and CSS were found to be 6.45, 8.3, 6.25 and 7.01 respectively. SEM revealed presence of

micro-pores and irregular distribution of clumps on both media. Leaching test revealed that

CSS leached more of copper, iron and nickel after 48 and 72 hours exceeding consent values

for environmental discharge. Only iron exceeded consent values on MGS leachate after 48

hours while the other media had leaching concentrations not exceeding permissible values.

The maximum adsorption capacities of copper smelter slag were 3.3 mg g-1 media, 3.1, mg g-1

media and 3.2 mgg-1 media for the removal of iron, copper and nickel ions respectively after

30 minutes. In the case of MGBW, the optimal capacities were 7.6 mg g-1 media, 6.7 mg g-1

media and 6.2 mg g-1 media respectively, for iron, copper and nickel removal after 45

minutes. However, maximum adsorption capacities for MGS were found to be 6.7, 6.1 and

4.5 mgg-1 media respectively for copper, iron and nickel after 45 minutes. As for CBW

maximum adsorption capacities were 8.5, 8.7 and 4.2 mgg-1 media for copper, iron and nickel

respectively after 45 minutes. Both Pseudo First and Pseudo Second Order models described

the adsorption process. Intra-particle and mass transfer diffusion were both rate controlling

the reactions. Freundlich and Langmuir isotherm models were involved in adsorption process

indicating that adsorption of some metals was taking place in some heterogeneous and

homogenous active sites. Thermodynamic parameters for CSS, MGS, CBW and MGBW

indicated that the adsorption process was non spontaneous process and was exothermic.

Reusability or regeneration studies on MGBW, MGS, CBW and CSS verified that CBW

lowered its original capacity in three regeneration cycles using 0.1 M Sodium Hydroxide.

Based on performance of media two media, CBW and MGBW were selected for column

studies. Column results revealed that, nickel was leaching from MGBW and less removed

due to large ionic radius and high electronegativity compared to other metals. However,

CBW column results indicated better adsorptive removal of target metal ions. Thomas

column kinetic model described the mechanism for adsorptive removal of divalent copper,

iron and nickel better in the fixed bed column study and it agreed with the some batch models

as the Thomas model predicts that the adsorption process follows Langmuir isotherm model

and was derived based on the second order kinetics. Overall, MGBW and CBW can be

applied as low cost, effective and environmentally friendly adsorbents for the adsorptive

removal of copper, iron and nickel irons from wastewater. However, CSS and MGS can also

be used for separation of heavy metals from wastewater provided they are modified. However

further studies on MGS and CSS through fixed bed column process should be investigated

before field trials. It is also however important that further studies should be done using real

wastewater before field trials.