Keywords

1 Introduction

The available resource recovery processes have capital and operating expenses that are higher than what the revenue from the recovered metal can support. In order to recover the copper value from metallurgical wastes such as copper anode slimes, copper slags, waste copper dust (WCD), the copper smelting industry is becoming more and more interested in inventing ways for doing so. It would be advantageous to have a processing technique that could eliminate impurities from the WCD while maintaining a suitable level of revenue metals in the resultant concentrate.

To facilitate the management of accumulated WCD, it would be desirable if this could be done economically. It is believed that recovering copper as oxides of nanoparticles (CuO-NPs) from purified pregnant leach solution (PPLS) is preferable to recovering it as cathode slabs [1]. This is because CuO-NPs outperform conventional copper oxide in many applications thanks to their exceptional physicochemical characteristics. Recently, there has been increased interest in producing CuO-NPs with p-type semiconductivity [2]. CuO-NPs are recognized as one of the best inorganic semiconductors with desirable properties [3].

Moreover, CuO-NPs can be used in a wide range of technological applications, such as gas sensors [4, 5], magnetic phase transmitters [6], heterogeneous catalysts [7,8,9], and optical switches [6, 10, 11], nanofluids [12, 13], solar energy transformer [4, 14], lithium ion electrode materials [8, 15], and field emitter [6, 11].

Due to the vast range of uses for metallic/metallic oxide nanoparticles, numerous methods for manufacturing them via chemical, physical, and biological processes have also been documented (CuO-NPs). Sol-gel [16], wet chemical approaches [17, 18], thermal oxidation of Cu substrates [10], and solvothermal methods [4, 6], microwave irradiation [19], sonochemical [20], and microemulsion [21], electrochemical [22], hydrothermal [23, 24], solid-state reaction [25, 26], submerged arc [27], and precipitation methods [12, 28, 29] are a few examples of these techniques. Co-precipitation and the thermal degradation of precursors are additional methods for producing nanoparticles [28, 30,31,32].

A key consideration in selecting the best technique is how to generate copper or copper oxide nanoparticles with an acceptable level of purity [27]. In a closed vessel, such as an autoclave, solvents are heated significantly above their boiling temperatures in a solvothermal process that involves chemical interaction. When water is used as the solvent, the process is referred to as a hydrothermal one. A variety of literatures have discussed how this strategy is used [33, 34]. Byrappa and Yoshimura [35] described the hydrothermal process as a process involving a heterogeneous chemical reaction in a closed system, in the presence of an aqueous or non-aqueous solvent above room temperature, and at pressures more than 1 atm.

When water is 647.15 K and 221 bar above atmospheric pressure, it is referred to as a supercritical fluid. Water or other fluids that are supercritical behave both like liquids and like gases. Surface tension is decreased when a solid and a supercritical fluid come into contact, and chemical compounds that are extremely difficult to dissolve in ambient conditions are also dissolved. These techniques largely take use of the metal’s higher solubility and reactivity [36]. There are many advantages to using supercritical conditions, including simplicity, very small grain size, the presence of a single phase, and the creation of high-purity nanocrystals with outstanding crystallinity and green properties [37].

The thermal reduction technique is an illustration of a solvothermal process. This technology exceeds older ones like the chemical reduction method in terms of cleanliness, speed, and cost despite being relatively new. It requires the appropriate precursor to be picked, as well as focused heating. Numerous studies have shown that this method can produce copper oxide nanoparticles. According to Zhang et al. [8], the thermal breakdown of the copper oxalate precursor produced CuO-NPs with an average diameter of 10 nm. CuO nanoparticles were also produced from the thermal breakdown of the precursors brochantite Cu4(SO4)(OH)6 and posnjakite Cu4(SO4)(OH)6.H2O [38]. Simpleness, a high possibility of single-phase, high-purity nanocrystals with high crystallinity, low particle size, and favourable environmental effects are all guaranteed by this method [27, 37].

A few studies have been done on the production of CuO-NPs by the thermal breakdown of copper precursors in a CSD’s leach solution [27, 32, 38]. Additionally, the thermal decomposition method for creating CuO-NPs from CSD requires careful selection of a copper precursor, as was previously mentioned in the preceding paragraphs [27]. Therefore, it is essential to optimize the process parameters of agitation speed, temperature, flow rate, and concentration of both Na2CO3 and CuSO4 in order to obtain the best copper precursor, which will support the production of CuO-NPs with enhanced grade and recovery during its thermal decomposition.

Thus, this chapter presents the results of the inquiry into the production of CuO-NPs from this low-grade waste metal dust (i.e. CSD).

2 Experimental Method

2.1 Material

2.1.1 Waste Metal Dust

The WCD from South Africa served as the waste metal dust in this investigation.

2.2 Methods

2.2.1 Production of Pregnant Leach Solution (PPLS)

In Okanigbe [39], the method for creating the PPLS employed in the synthesis of the CuO-NPs is described.

2.2.2 Design of Experiment and Procedure for Production of Copper Precursor

Starting with the manufacture of copper precursor from PPLS, CuO-NP manufacturing began. The 3-by-2 complete factorial experimental design approach was used to create the experiment design for the manufacture of copper precursor from PPLS, as illustrated in Tables 6.1 and 6.2.

Table 6.1 Parameters considered for the production of copper precursor
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Table 6.2 Design of experiment for the production of copper precursor
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The copper precursor was made by adding 2 M Na2CO3 solution dropwise to 0.2 M CuSO4 solution in a 500-ml conical flask that was set on a hot plate while the mixture was stirred with a magnetic stirrer at various temperatures (Fig. 6.1). Filtration was used to separate the resultant green precipitate, which was then washed with distilled water and pure ethanol. Then, for 24 h, this green precipitate is dried in an oven at 105 °C.

Fig. 6.1
A photograph of an experimental setup with instruments captioned as a hotplate, magnetic rod, C U S O 4 solution, conical flask, tripod stand, N A C O 3, and separating funnel. The conical flask on the bottom contains C U S O 4 solution while the separating funnel on the top contains N A C O 3 solution.

Experimental setup for the production of copper precursor

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2.2.3 Design of Experiment and Procedure for Production of CuO-NPs from Copper Precursor

Using a thermogravimetric analyser and an atmospheric flow, it was determined how the synthetized copper precursor behaved thermally. Thirty-five milligrams of samples was placed in a platinum crucible on the microbalance pan and heated between 25 and 1000 °C at rates of 5, 10, 15, and 20 °C/min.

The 3-by-2 complete factorial experimental design method was used to create the study (Tables 6.1 and 6.2). Soon after becoming familiar with the copper precursor’s thermal behaviour, the experiment was planned using the data, as can be seen in Tables 6.3 and 6.4 for the production of CuO-NPs. Experimental procedure can be found in Okanigbe [39].

Table 6.3 Parameters considered for the production of CuO-NPs
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Table 6.4 Design of experiment for production of copper nanoparticles
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3 Results and Discussion

3.1 Mineralogy of Copper Precursor

This investigation into the synthesis of CuO-NPs from low-grade waste metal dust PPLS from South African CSD focuses on the synthesis and characterization of copper precursors before thermally decomposing the copper precursors to produce CuO-NPs. The many physical and chemical techniques used for material characterization are summarized in this section. Various physical characterization techniques, including powder X-ray diffraction, SEM, and TEM, were used to evaluate the copper precursor and CuO-NPs samples that were produced.

According to published literatures [27, 32, 40, 41], the thermal dehydration and desulpheration processes (Eqs. 6.1–6.3) are part of the reaction pathway that leads to copper (II) oxide. Equations 6.1–6.3 demonstrate that the three separate steps of the decomposition of CuSO4 in solution were dehydration (Eq. 6.1), crystallization (Eq. 6.2), and desulphurization (Eq. 6.3) according to Koga et al. [41].

$$ {Cu}_4\left({\textrm{SO}}_4\right){(OH)}_6.x{\textrm{H}}_2\textrm{O}{\to}^{170-180{}^{\circ}\textrm{C}}\to CuS{\textrm{O}}_4.3 Cu{(OH)}_2+{x\textrm{H}}_2\textrm{O} $$
(6.1)
$$ CuS{\textrm{O}}_4.3 Cu{(OH)}_2{\to}^{170-180{}^{\circ}\textrm{C}}\to CuS{\textrm{O}}_4.2 Cu{(OH)}_2+ CuO+{x\textrm{H}}_2\textrm{O} $$
(6.2)
$$ CuS{\textrm{O}}_4.2 Cu{(OH)}_2{\to}^{170-180{}^{\circ}\textrm{C}}\to CuO+{x\textrm{H}}_2\textrm{O}+{\textrm{SO}}_2+\frac{1}{2}{\textrm{H}}_2\textrm{O} $$
(6.3)

3.1.1 Mineralogy of Copper Precursor Produced Under TC 25 °C/340 rpm

The XRD machine was used to characterize the crystal structure and phase purity of the copper precursor generated under TC of 25 °C/340 rpm (Table 6.2). Figure 6.2 demonstrates that exactly 87.1% of all the diffraction peaks were indexed to hydrotalcite, while 4.8% of the peaks were indexed to aragonite, and the remaining 8.2% of the peaks were indexed to the copper-containing compounds 0.1% posnjakite and 8.1% cuprite.

Fig. 6.2
A X R D graph with counts versus position illustrates Bragg's peaks for hydrotalcite 87.1%, aragonite 4.8%, posnjakite 0.1%, langite 0.0%, and cuprite 8.1%.

XRD result of copper precursor obtained under 25 °C/340 rpm TC

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3.1.2 Mineralogy of Copper Precursor Produced Under TC 25 °C/740 rpm

Figure 6.3 displays the crystal structure and phase purity of the copper precursor produced at TC of 25 °C/740 rpm (Table 6.2). The majority of the diffraction peaks, 82.9%, were attributed to hydrotalcite, while 5.0% is indexed to aragonite. The remaining 0.1% and 12.1% of the peaks were attributed to the copper-containing minerals posnjakite and cuprite, respectively.

Fig. 6.3
A X R D graph with counts versus position illustrates Bragg's peaks for hydrotalcite 82.9%, aragonite 5.0%, posnjakite 0.1%, langite 0.0%, and cuprite 12.1%.

XRD result of copper precursor obtained under 25 °C/740 rpm TC

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3.1.3 Mineralogy of Copper Precursor Produced Under TC 25 °C/1480 rpm

XRD was used to characterize the crystal structure and phase purity of the copper precursor generated under TC of 25 °C/340 rpm (Table 6.2). As can be seen in Fig. 6.4, hydrotalcite accounted for exactly 86.5% of all the diffraction peaks, while 4.5% of them were indexed to aragonite, the other diffraction peaks were indexed to posnjakite (0.1%) and cuprite (9.0%).

Fig. 6.4
A X R D graph with counts versus position illustrates Bragg's peaks for hydrotalcite 86.5%, aragonite 4.5%, posnjakite 0.1%, langite 0.0%, and cuprite 9.0%.

XRD result of copper precursor obtained under 25 °C/1480 rpm

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3.1.4 Mineralogy of Copper Precursor Produced Under TC 55 °C/340 rpm

By using the XRD, the crystal structure and phase purity of the copper precursor produced at TC of 55 °C/340 rpm (Table 6.2) were identified. According to Fig. 6.5, the exact percentage of diffraction peaks indexed to hydrotalcite was 92.3%, the percentage indexed to aragonite was 2.7%, and the percentage indexed to cuprite was 5.1%.

Fig. 6.5
A X R D graph with counts versus position illustrating Bragg's peaks for hydrotalcite 92.3%, aragonite 2.7%, posnjakite 0.0%, langite 0.0%, and cuprite 5.1%.

XRD result of copper precursor obtained under 55 °C/340 rpm

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3.1.5 Mineralogy of Copper Precursor Produced Under TC 55 °C/740 rpm

XRD was used to characterize the crystal structure and phase purity of the copper precursor generated under TC of 55 °C/740 rpm (Table 6.2). Figure 6.6 demonstrates that exactly 88.1% of all the diffraction peaks were indexed to hydrotalcite, while 3.0% of the peaks were indexed to aragonite, and the remaining 0.1% and 8.8% of the peaks were indexed to cuprite.

Fig. 6.6
A X R D graph with counts versus position illustrating Bragg's peaks for hydrotalcite 88.1%, aragonite 3.0%, posnjakite 0.1%, langite 0.0%, and cuprite 8.8%.

XRD result of copper precursor obtained under 55 °C/740 rpm

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3.1.6 Mineralogy of Copper Precursor Produced Under TC 55 °C/1480 rpm

XRD was used to characterize the crystal structure and phase purity of the copper precursor generated under TC of 55 °C/1480 rpm (Table 6.2). As can be seen in Fig. 6.7, hydrotalcite accounted for exactly 89.5% of all the diffraction peaks, while 2.6% of them were indexed to aragonite, the other diffraction peaks were indexed to the copper-containing compounds posnjakite (0.3%), langite (0.1%), and cuprite (7.5%).

Fig. 6.7
A X R D graph with counts versus position illustrating Bragg's peaks for hydrotalcite 89.5%, aragonite 2.6%, posnjakite 0.3%, langite 0.1%, and cuprite 7.5%.

XRD result of copper precursor obtained under 55 °C/1480 rpm

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3.1.7 Mineralogy of Copper Precursor Produced Under TC 85 °C/340 rpm

The copper precursor produced at TC 85 °C/340 rpm (Table 6.2) was examined using the XRD apparatus for its crystal structure and phase purity. According to Fig. 6.8, precisely 68.3% of all the diffraction peaks were indexed to hydrotalcite, 11.0% to aragonite, and the remaining peaks were indexed to posnjakite (4.8%) and cuprite (15.9%).

Fig. 6.8
A X R D graph with counts versus position illustrating Bragg's peaks for hydrotalcite 68.3%, aragonite 11.0%, posnjakite 4.8%, and cuprite 15.9%.

XRD result of copper precursor obtained under 85 °C/340 rpm

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3.1.8 Mineralogy of Copper Precursor Produced Under TC 85 °C/740 rpm

The XRD machine was used to characterize the crystal structure and phase purity of the copper precursor generated under TC of 85 °C/740 rpm (Table 6.2). Figure 6.9 reveals that exactly 83.2% of all the diffraction peaks were indexed to hydrotalcite, while 3.5% of the peaks were indexed to aragonite, and the remaining 13.3% of the peaks were indexed to posnjakite (0.1%) and cuprite (13.2%).

Fig. 6.9
A X R D graph with counts versus position illustrating Bragg's peaks for hydrotalcite 83.2%, aragonite 3.5%, posnjakite 0.1%, langite 0.0%, and cuprite 13.2%.

XRD result of copper precursor obtained under 85 °C/740 rpm

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3.1.9 Mineralogy of Copper Precursor Produced Under TC 85 °C/1480 rpm

The crystal structure and phase purity of the copper precursor produced at TC of 85 °C/1480 rpm (Table 6.2) are shown in Fig. 6.10. 70.3% of the diffraction peaks were attributable to hydrotalcite, whereas aragonite was responsible for 10.6% of the peaks. Posnjakite, langite, and cuprite are the copper-containing minerals that are responsible for the remaining diffraction peaks, 5.8%, 1.6%, and 11.7%, respectively.

Fig. 6.10
A X R D graph with counts versus position illustrating Bragg's peaks for hydrotalcite 70.3%, aragonite 10.6%, posnjakite 5.8%, langite 1.6%, and cuprite 11.7%.

XRD result of copper precursor obtained under 85 °C/480 rpm

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3.1.10 Optimum TC for Production of Copper Precursor

It is shown that the amount of copper-containing compounds (CCC) in the copper precursor obtained from the PPLS of low-grade waste metal dust (i.e. CSD) can be measured accurately by using the TC of temperature and agitation speed (Table 6.2). Based on the results obtained (Table 6.5), the optimum TC that produced the highest CCC (20.7%) is 85 °C/340 rpm (Fig. 6.11).

Table 6.5 Percentage mineralogical composition of copper precursor
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Fig. 6.11
A clustered bar graph illustrates % content versus treatment combinations. 9 bar clusters illustrate posnjakite, langite, and cuprite % for different treatment conditions. The bars for cuprite have the highest peak among the three. The highest value occurs at 85 degrees at 340 r p m.

Percentage content of copper-containing compounds in copper precursor at different TC

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The variation in percentage contents of hydrotalcite and aragonite in copper precursor can be seen in Table 6.5. Based on the results obtained in Table 7.5, the highest combination of hydrotalcite (92.3%) and aragonite (2.7%) contents, none-copper-containing compounds is obtained under TC 55 °C/340 rpm (Fig. 6.12) while the least combination of hydrotalcite (68.3%) and aragonite (11.0%) contents is obtained under TC 85 °C/340 rpm (Fig. 6.12); this is consistent with the claim of optimum TC for production copper precursor is 85 °C/340 rpm (Table 6.5).

Fig. 6.12
A bar graph illustrates % content versus treatment combinations. 9 treatment combinations are illustrated in the form of paired bars illustrating hydrotalcite and aragonite %. The highest peak is shown at 55 degrees at 740 r p m and bars for hydrotalcite always have a higher value than aragonite.

Percentage content of hydrotalcite and aragonite in copper precursor at different TC

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3.2 Mineralogy of Copper Oxide Nanoparticles

The copper precursor that was produced under optimum TC (Table 6.5) was used as the starting material for the production of the copper oxide nanoparticles (CuO-NPs). This copper precursor was subjected to the TC in Table 6.4. The results of the TC are reported in the subsequent part of this paper.

3.2.1 Mineralogy of CuO-NPs Produced under 650 °C/1 h

The XRD machine was used to characterize the crystal structure and phase purity of the CuO-NPs generated under TC of 650 °C/1 h (Table 6.4). Figure 6.13 demonstrates that exactly 47.2% of all the diffraction peaks were indexed to tenorite, while 12.5%, 15.4%, 16.0%, 5.4%, and 3.6% of the remaining peaks were indexed to the none-copper-containing compounds, which are magnetite, sodium aluminium phosphate, disodium calcium silicate, grossular ferrian, periclase, respectively.

Fig. 6.13
A X R D graph with counts versus position illustrates Bragg's peaks for tenorite 47.2%, magnetite 12.5%, sodium aluminium phosphate 15.4%, disodium calcium silicate 16.0%, grossular ferrian 5.4%, and periclase 3.6%.

XRD result of CuO-NPs obtained under 650 °C/1 h

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3.2.2 Mineralogy of CuO-NPs Produced under 650 °C/2 h

The CuO-NPs produced under TC of 650 °C/2 h (Table 6.4) were characterized in terms of their crystal structure and phase purity using an XRD machine. Figure 6.14 shows that exactly 46.7% of all the diffraction peaks were indexed to tenorite, while the remaining peaks were indexed to the non-copper-containing substances, such as magnetite, sodium aluminium phosphate, disodium calcium silicate, grossular ferrian, and periclase, at rates of 14.0%, 15.8%, 11.6%, 8.1%, and 3.8%, respectively.

Fig. 6.14
A X R D graph with counts versus position illustrates Bragg's peaks for tenorite 46.7%, magnetite 14.0%, sodium aluminium phosphate 15.8%, disodium calcium silicate 11.6%, grossular ferrian 8.1%, and periclase 3.8%.

XRD result of CuO-NPs obtained under 650 °C/2 h

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3.2.3 Mineralogy of CuO-NPs Produced under 650 °C/3 h

Using the XRD machine, the CuO-NPs produced at TC of 650 °C/3 h (Table 7.4) were examined for their crystal structure and phase purity. Figure 6.15 demonstrates that exactly 50.1% of all the diffraction peaks were indexed to tenorite, while the remaining peaks were indexed, at percentages of 12.8%, 14.9%, 13.1%, 5.4%, and 3.8%, to the non-copper-containing materials, such as magnetite, sodium aluminium phosphate, disodium calcium silicate, grossular ferrian, and periclase, respectively.

Fig. 6.15
A X R D graph with counts versus position illustrates Bragg's peaks for tenorite 50.1%, magnetite 12.8%, sodium aluminium phosphate 14.9%, disodium calcium silicate 13.1%, grossular ferrian 5.4%, and periclase 3.8%.

XRD result of CuO-NPs obtained under 650 °C/3 h

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3.2.4 Mineralogy of CuO-NPs Produced Under 750 °C/1 h

CuO-NPs generated at TC of 750 °C/1 h (Table 7.4) were subjected to XRD analysis to determine the crystal structure and phase purity. Figure 6.16 shows that exactly 48.7% of all the diffraction peaks were indexed to tenorite, while the remaining peaks were indexed to non-copper-containing compounds like magnetite, sodium aluminium phosphate, disodium calcium silicate, grossular ferrian, and periclase at percentages of 8.8%, 13.0%, 17.5%, 8.6%, and 3.4%, respectively.

Fig. 6.16
A X R D graph with counts versus position illustrates Bragg's peaks for tenorite 48.7%, magnetite 8.8%, sodium aluminium phosphate 13.0%, disodium calcium silicate 17.5%, grossular ferrian 8.6%, and periclase 3.4%.

XRD result of CuO-NPs obtained under 750 °C/1 h

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3.2.5 Mineralogy of CuO-NPs Produced Under 750 °C/2 h

To ascertain the crystal structure and phase purity of CuO-NPs produced at TC of 750 °C/2 h (Table 6.4), XRD analysis was performed. Figure 6.17 demonstrates that exactly 51.3% of all diffraction peaks were assigned to tenorite, while the remaining peaks were assigned to non-copper-containing substances like magnetite, sodium aluminium phosphate, disodium calcium silicate, grossular ferrian, and periclase at percentages of 12.0%, 17.8%, 10.1%, 6.0%, and 2.7%, respectively.

Fig. 6.17
A X R D graph with counts versus position illustrates Bragg's peaks for tenorite 51.3%, magnetite 12.0%, sodium aluminum phosphate 17.8%, disodium calcium silicate 10.1%, grossular ferrian 6.0%, and periclase 2.7%.

XRD result of CuO-NPs obtained under 750 °C/2 h

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3.2.6 Mineralogy of CuO-NPs Produced Under 750 °C/3 h

XRD examination was done to determine the crystal structure and phase purity of CuO-NPs produced at a TC of 750 °C/3 h (Table 6.4). According to Fig. 6.18, tenorite accounted for exactly 50.8% of all diffraction peaks, with the remaining peaks being assigned to non-copper-containing materials like magnetite, sodium aluminium phosphate, disodium calcium silicate, grossular ferrian, and periclase at percentages of 11.1%, 16.8%, 13.2%, 6.2%, and 1.9%, respectively.

Fig. 6.18
A X R D graph with counts versus position illustrates Bragg's peaks for tenorite 50.8%, magnetite 11.1%, sodium aluminium phosphate 16.8%, disodium calcium silicate 13.2%, grossular ferrian 6.2%, and periclase 1.9%.

XRD result of CuO-NPs obtained under 750 °C/3 h

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3.2.7 Mineralogy of CuO-NPs Produced Under 850 °C/1 h

CuO-NPs generated at a TC of 850 °C/1 h (Table 6.4) were subjected to an XRD investigation to ascertain their crystal structure and phase purity. Tenorite accounted for exactly 51.3% of all diffraction peaks. The remaining peaks were ascribed to non-copper-containing substances such as magnetite, sodium aluminium phosphate, disodium calcium silicate, and grossular ferrian, at percentages of 14.4%, 17.7%, 11.4%, and 5.2%, respectively. These are all shown in Fig. 6.19.

Fig. 6.19
A X R D graph with counts versus position illustrates Bragg's peaks for tenorite 51.3%, magnetite 14.4%, sodium aluminium phosphate 17.7%, disodium calcium silicate 11.4%, and grossular ferrian 5.2%.

XRD result of CuO-NPs obtained under 850 °C/1 h

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3.2.8 Mineralogy of CuO-NPs Produced Under 850 °C/2 h

An XRD analysis was performed on CuO-NPs produced at a TC of 850 °C/2 h (Table 6.4) to determine their crystal structure and phase purity. Exactly 48.9% of all diffraction peaks were accounted for by tenorite. The remaining peaks, with percentages of 15.9%, 14.9%, 14.4%, and 5.9%, were attributed to non-copper-containing materials such as magnetite, sodium aluminium phosphate, disodium calcium silicate, and grossular ferrian. All of these are displayed in Fig. 6.20.

Fig. 6.20
A X R D graph with counts versus position illustrates Bragg's peaks for tenorite 48.9%, magnetite 15.9%, sodium aluminium phosphate 14.9%, disodium calcium silicate 14.4%, and grossular ferrian 5.9%.

XRD result of CuO-NPs obtained under 850 °C/2 h

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3.2.9 Mineralogy of CuO-NPs Produced Under 850 °C/3 h

CuO-NPs produced at a TC of 850 °C/3 h (Table 6.4) were subjected to an XRD investigation to ascertain their crystal structure and phase purity. Tenorite accounted for exactly 47.0% of all diffraction peaks. Non-copper-containing substances including magnetite, sodium aluminium phosphate, disodium calcium silicate, and grossular ferrian were blamed for the remaining peaks, which had percentages of 16.8%, 10.9%, 17.9%, and 7.5%. These are all shown in Fig. 6.21.

Fig. 6.21
A X R D graph with counts versus position illustrates Bragg's peaks for tenorite 47.0%, magnetite 16.8%, sodium aluminium phosphate 10.9%, disodium calcium silicate 17.9%, and grossular ferrian 7.5%.

XRD result of CuO-NPs obtained under 850 °C/3 h

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3.2.10 Optimum TC for Production of CuO-NPs

It is shown that the amount of copper compound (CC) in the CuO-NPs obtained from the copper precursor produced from the WCD can be measured accurately by using the TC of temperature and agitation speed (Table 6.4). Based on the results obtained (Table 6.6), the optimum TC that produced the highest CC (51.3%) is 750 °C/2 h (Fig. 6.22).

Table 6.6 Summary of mineralogical composition of CuO-NPs at different TC
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Fig. 6.22
A bar graph for % content of tenorite versus 9 different treatment conditions. The highest peaks are observed for treatment conditions at 750 degrees for 2 hours and 850 degrees for 1 hour.

Percentage content of CC in CuO-NPs at different TC

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The variation in percentage contents of magnetite, sodium aluminium phosphate, disodium calcium silicate, grossular ferrian, and periclase in CuO-NPs can be seen in Table 6.6. Based on the results obtained in Table 6.6, the highest combination of magnetite (14.0%), sodium aluminium phosphate (15.8%), disodium calcium silicate (11.6%), grossular ferrian (8.1%), and periclase (3.8%), none-copper-containing compounds (NCCC) is obtained under TC 650 °C/2 h (Fig. 6.23) while the least combination of magnetite (12.0%), sodium aluminium phosphate (17.8%), disodium calcium silicate (10.1%), grossular ferrian (6.0%), and periclase (2.7%) contents is obtained under TC 750 °C/2 h (Fig. 6.23); this is consistent with the claim of optimum TC for production Cu-NPs is 750 °C/2 h (Table 6.6).

Fig. 6.23
A bar graph for total N C C C versus 9 different treatment conditions illustrates the highest peaks at 650 degrees celsius for 2 hours and 850 degrees celsius for 3 hours.

Percentage content of NCCC in CuO-NPs at different TC

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3.3 Characterization of CuO-NPs

3.3.1 SEM

The morphology of the CuO-NPs powder was examined using the SEM machine (Fig. 6.24). The SEM images indicate that the particles are flower like in shape. Temperature is observed to play an important part in the morphology of the developed CuO-NPs, presupposing that the shape of the CuO-NPs can be tuned by changing the temperature.

Fig. 6.24
8 S E M scans illustrate clustered quatrefoil-like structures with different magnifications. The structures illustrate the shapes of developed copper oxide nanoparticles.

SEM images showing the flower like shape of developed CuO-NPs observed under (a and b) 10, 000x, (c and d) 20,000×, (e and f) 30,000×, and (g and h) 40,000× magnifications

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3.3.2 TEM

The TEM images in Fig. 6.25 show no specific defect and average crystallite size is estimated as 35 ± 5 nm. The TEM images indicate that the particles are cube like in shape.

Fig. 6.25
8 T E M scans illustrate structures of copper oxide nanoparticles. The scans have markings illustrating the scale as 100 or 200 nanometers. The structures appear as cloud-like dense patches on a bright surface.

TEM images of the CuO-NPs [A-H], produced from WCD

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4 Conclusions

The aim of the study was to develop CuO-NPs from leach solution of low-grade WCD. Several deductions were reached in the course of this study. Amongst these deductions are the following:

  1. 1.

    The optimum TC that produced the highest copper-containing compounds in the copper precursor (20.7%) is 85 °C/340 rpm.

  2. 2.

    The optimum TC that produced the highest copper compound in the CuO-NPs (51.3%) is 750 °C/2 h.

  3. 3.

    Angulars to spherical CuO-NPs were successfully prepared by thermal decomposition method with mean diameter of 35 ± 5 nm.

These results represent a trend towards optimum experimental conditions aimed at maximizing CuO-NPs output and minimizing contaminants. It can be concluded that since this method does not require organic solvents, expensive raw materials, and complicated equipment, it is superior to the other methods for the synthesis of CuO-NPs from leach solution (i.e. CuSO4 solution) of low-grade WCD.