1 Introduction

Increased utilization of energy and resources worldwide has produced encouraging but unsustainable development [1]. This has generated the need for a more sustainable use of alternative resources and a reduction in energy consumption [2]. One major way of achieving this is the reuse of waste in product development [3]. Agro-waste biomass has been considered as a viable route to material synthesis for sustainable development [4]. According to Wang, Li [5], agro-wastes are broadly classified as lignocellulosic and non-lignocellulosic in nature. Their non-lignocellulosic types, like chicken feather [6], cow bone [7], cow-horn [8], and other related products are generally considered affordable and easily available for research and development in the synthesis of inorganic metallic oxides [9]. Moreover, the use of locally sourced lignocellulosic and non-lignocellulosic biomass materials has been proven as a novel, low-cost, and highly efficient adsorbent [10, 11], which can be used for the absorption of heavy metals in wastewater [12], and other aqueous solutions [13, 14].

According to the United Nation Environmental Program (UNEP, 2007), about 140 billion metric tons of waste from biomass is generated across the globe in the agricultural sector. Annually, approximately 8.5 million tons of chicken feathers are produced worldwide [15]. Chicken feather contains approximately 95-98% protein, primarily β-keratin, as well as numerous functional groups such as carboxyl, hydroxyl, amidogen, and sulfhydryl [16, 17]. The Keratin component of chicken feather makes it non-lignocellulosic, and if theses wastes are not properly managed, they will lead to environmental hazard [18]. In Nigeria, poultry waste has been identified as a major source of concern, with a large amount of it generated each year, with chicken feathers being a major component [19].

Gasification and other related thermochemical routes for waste chicken feather management have been previously reported [20, 21]. With an associated risk of toxic gases like HCl, SO2, NO2 and NO being released alongside useful energy and material recovery [22, 23]. Although dusters, decorative products, and high-end bedding like pillows, mattresses, etc. are produced from feather waste, most of these wastes still end up in landfills, incinerators, dump sites, etc., and they generate greenhouse gases, thus contaminating the environment [19, 24, 25]. Furthermore, as the world’s population grows and energy needs cannot be met within the constraints of rapidly depleting and expensive fossil fuels, the search for optimal links between energy indices and biofuel production from non-lignocellulosic biomass such as chicken feathers becomes a strong call to action [26,27,28]. The valorisation of chicken feathers becomes the focus of this study with the dual proceeds of energy recovery and solid waste recycling. This has necessitated the development of alternative waste management routes that are more integrated and benign.

Recently, several efforts have been made to find various alternatives for managing chicken feather wastes, such as using them as bio-fertilizers [15, 29], bio-fuel [30], and particularly for healing wounds in biomedical applications [25]. Zhan, Wool [31] fabricated composite using chicken feather fibre, E-glass fibre and epoxy. Their properties were investigated as potential printed circuit boards. They found out that the electrical resistivity of chicken feathers was higher than that of E-glass fibre by about two-four orders of magnitude. The dielectric constant decreases as the fiber content of the composite decreases. It was concluded that the chicken feather could find potential use in the printed circuit board industry. Also, chicken feathers were used by Pal, Alsuwaidi [24] as an adsorbent for methyl diethanolamine. The equilibrium adsorption fitted the Freundlich model at 298 K, with 525 mg/g as the maximum uptake capacity, and the Pseudo-Second-Order model fitted best for the kinetic analysis. Chicken feathers were found to be recyclable with a high total organic acid uptake capacity even after five cycles. The study confirmed chicken feather as a low-cost alternative to commercial activated carbon absorbents for cleaning lean methyl diethanolamine aqueous solutions from their heat-stable salts (HSS) contaminants.

Although the metallic oxide recovery from other non-lignocellulosic biomass like cow bone [9], and poultry litter [26] was recently reported for their possible applications in adsorption and other catalysis related applications, the distinctive features possessed by chicken feathers, including low density, high flexibility, compressibility, excellent thermal properties, and chemically insoluble in organic solvents, have not been considered [32]. These justify its choice for this study. This study, however, focuses on the recovery of metallic oxide-rich biochar from chicken feather waste using a retort-heated top-lit updraft reactor. It’s a low-temperature self-regulated reactor that uses waste biomass as a source of energy. Such studies are highly significant in developing economies, where energy costs and availability are recurring challenges.

2 Methodology

2.1 Sourcing and purification of the sample

Chicken feathers were gotten as poultry waste from Unity Chicken Market in Ilorin, Nigeria. It was washed to remove sand and other impurities and sun dried. It was further oven dried to remove other moisture content entrapped in the waste at 105 °C for 3 hrs using an electric oven. It was then loaded into a retort heating chamber to convert it to metal oxide.

2.2 Production of metal oxide rich biochar

For this research, a stainless-steel top-lit gasifier biomass conversion reactor, as illustrated in Fig. 1 was utilized. The size, setup, description, and operation of the reactor were all provided in detail by Adeniyi and Ighalo [2]. The inner chamber of the reactor was loaded with a weighed amount of chicken feathers, and the space between the inner chamber and the outer or bigger reactor was loaded with biomass waste as fuel. These fuels were arranged in layers to allow an updraft of oxygen from the reactor bottom to the combustion font to supply heat to the reactor. The system was allowed to burn for 2-3 minutes after being ignited from the top so as to allow the fire to circulate throughout all parts of the reactor before it was covered with a lid, which gives room for exhaust of the fume. This was done in an open environment and the experiment ended when equilibrium was reached at ambient temperature when the combustion fuel burned to ash and the chicken feathers transformed into metal oxide rich biochar [33]. The product was weighed and stored in an airtight container.

Fig. 1
figure 1

Description of the Process for Metal Oxide Rich (MOR) Biochar Production

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2.3 Characterization of MOR biochar

The metallic oxide produced from chicken feathers was characterized using Brunauer-Emmett-Teller (BET) (Quantachrome NovaWin©1994-2013, Quantachrome instruments version 11.03) to determine the pore area, specific pore volume, and specific surface area by N2 adsorption isotherms at 77 K, pore area, and specific pore volume. The biochar sample was degassed at a temperature of 120 °C for 3 h. In addition, the surface area was calculated based on the nitrogen adsorption-desorption isotherm obtained from the Multipoint BET analysis, whilst the total pore volume and pore diameter were obtained using the Barette, Jovner, and Halenda (BJH) method [34, 35]. The surface morphology was determined using Scanning Electron Microscopy (SEM). The acceleration voltage of the microscope was set to 15 kV and magnification of 500–1000 times. Fourier Transform Infrared Spectroscopy FTIR (Scimadzu, FTIR-8400S, Nigeria) was used to elucidate the functional groups present. The spectrum was recorded using the transmittance method in the 4000–650 cm− 1 region with 30 sample scans. The crystalline phase of the material was determined by X-ray diffraction (XRD). The XRD operates with Cu Kα emission (λ = 1.54105 Å, 45 kV, 40 mA per sec). Energy Dispersive Spectroscopy (EDS) was used for the elemental analysis, and X-ray fluorescence spectroscopy (XRF) was used for analysis of the minerals present in the sample.

3 Results and discussion

3.1 Temperature profile and MOR biochar yield

The process involves reusing heat generated by the controlled combustion of biomass residues (Daniella oliveri) in the conversion of waste chicken feathers into metal oxide-rich biochar in the innermost chamber. The temperature profile during the chicken feather to metal oxide conversion process is four point dependent. The four-point temperature profile of the reactor is given in Fig. 2. The four points, Ta, Tb, Tc, and Td, are the process temperatures monitored at the base (side), middle (side), top (side), and centre of the reactor respectively [36, 37]. Td provides the measured temperature with time within the reactor chamber while Ta, Tb and Tc captures the progress of the combustion zone within the heating zone as it proceeds from the top to the bottom of the reactor.

Fig. 2
figure 2

Temperature profile for the waste chicken feather conversion to metal oxide

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These four points were monitored with an infra-red thermometer to capture the thermal progression, thermal capacity, and recovery from the biomass residue employed to power the thermo-chemical conversion of the chicken feather to metal oxides. The summary of thermal characteristics and reactor performance criteria are presented in Table 1. The combustion was observed to have lasted for 90 minutes, with the peak temperature at 417.2 °C. It should be noted that the temperature of 250 °C was reached after 10 minutes of reactor operation, and thermal supply in this bracket was maintained for over 25 minutes. However, a more advanced temperature reading instrumentation facility would be needed to minimise the error in temperature reading associated with the autogenous temperature generation in the reactor. The biochar production of chicken feather-based metal oxide achieved a yield of 28.19%. In comparison with the yield of other biomass feedstocks produced from similar reactor configurations, a yield of 6.98% was obtained for the carbonization of plantain fibres after a carbonization duration of 150 minutes [38], a yield of 14.29% was obtained for the carbonization of elephant grass after a carbonization duration of 120 minutes [39], and a yield of 28.57% was obtained for the carbonization of Terminalia catappa leaves after a carbonization duration of 90 minutes [40]. The difference in the yield of the biochar produced in the auto-thermal carbonization reactor used in this study (apart from the biomass precursor type) is dependent on various factors such as the peak carbonization temperature and the carbonization duration, which are majorly controlled by environmental factors such as wind velocity and direction as well as the humidity of the environment. Variations in these environmental factors can affect the peak temperature reached by the reactor (for example, an increase in humidity would negatively affect the peak temperature) and the metal oxide biochar yield (as various studies have shown that in most cases, the yield of biochar is inversely proportional to the carbonization temperature).

Table 1 Summary of reactor performance
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The yield of the metal oxide from the waste chicken feather was computed using Eq. 1.

$${Yield}_{metal\ oxide}=\frac{m_{metal\ oxide}}{m_{raw}}\times 100\%$$
(1)

Where mraw = mass of waste chicken feathers = 200 g.

The yield of 28.19% metal oxide-rich biochar from waste chicken feathers is a moderate recovery of valuable material from the solid waste stream.

3.2 Textural properties of MOR biochar

Table 2 shows a summary of the textural properties of the metal oxide-rich biochar produced from waste chicken feathers. The BET analysis carried out shows that the sample gotten from the retort heating chamber is mesoporous in nature with a pore diameter of 2.132 nm. The biochar’s pore volume and the BET surface area obtained were 0.067 cc/g and 105.7 m2/g, respectively. In addition, the Langmuir surface area of the biochar obtained was 318.6 m2/g. This shows the material can be used as an active site for catalysis and also as an adsorbent for gases, ions, and molecules [41,42,43].

Table 2 Summary of textural properties of MOR biochar
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3.3 Fourier transform infrared spectroscopy FTIR

In order to determine the functional groups present in the sample, FTIR characterization was done, and the result is shown in Fig. 3, and Table 3 summarizes the adsorption bands. The peak at 3649.44 cm− 1 is attributed to the O-H group [44, 45]. For the N-H functional group, its peak was observed at 3479.70 cm− 1 which is from the keratin content of the sample [46]. This functional group was obtained in raw chicken at 3296.46 cm− 1 by Olawale and Okafor [47]. The peak at 2800.73 cm− 1 corresponds to the aliphatic stretching vibration of C-H [48]. A similar peak was obtained at 2962.76 cm− 1 for raw chicken feathers [47]. The peak at 2685.00 cm− 1 represents the thiol functional group, while the peak at 2252.93 cm− 1 indicates the isocyanate stretch of N=C=O. This peak was also observed to be present in waste raw chicken at 1238.34 cm− 1 [47]. The band located at 1743.71 cm− 1 adsorption band is that of the ester C-O group [49, 50]. This band was obtained at 1650 cm− 1 for waste raw chicken feathers [51]. The Peak at 1527.67 cm− 1 correspond to the presence of N-O Stretching of nitro compound. Peaks of 1172.76 cm− 1 is attributed to the S-O group while that at 1018.45 cm− 1 indicate the presence of C-C [52, 53]. The presence of sulphonate S-O asymmetrical and symmetrical stretch was observed at 1161.19 cm− 1 and 1032.11 cm− 1, respectively, in waste raw chicken feathers [47]. The peak at 856.42 cm− 1 can be attributed to calcite presence as confirmed in the XRF/EDS result [21], the peak at 709.83 cm− 1 could be attributed to C-S vibrations [52]. The biochar’s FTIR spectra show that they include a variety of functional groups that may influence how they are used for soil amendment [54]. The FTIR spectrum shows that the biochar contains sulphur-based compounds. Sulphur is beneficial to the soil because it promotes plant growth. It will acidify the soil, and some plants require a certain level of acidity in their soil [55, 56].

Fig. 3
figure 3

FTIR spectra of the sample

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Table 3 Summary of the adsorption bands of the sample
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3.4 Scanning electron microscopy (SEM)

The microstructure of the chicken feather biochar obtained from the retort heating process of the raw feather was analyzed using SEM micrographs (at magnification of 320x, 500x and 750x) and the results are shown in Fig. 4. The SEM micrographs of the chicken feather biochar show that it is composed of irregular-sized particles that agglomerate to give rise to a rough surface. The presence of irregular pores was also observed on the material’s surface. A rough structure was obtained as opposed to the smooth surface gotten by Oluba, Obi [57] as the keratin level increased in the bio-composite produced. This could be as a result of the metallic oxide or oxidized particles produced on the surface of the feather as the temperature increases in the presence of a limited supply of oxygen. A similar result was gotten by Belarmino, Ladchumananandasivam [58], albeit in an oven at 220 °C. Spaces (these are clearly shown at higher magnification), protein degradation and adherence of fragments to the surface as a result of the oxidation process were also observed in this work instead of the observed brittleness, cracks and hollowness (which was only noticeable at 3000 times magnification) surface by Belarmino, Ladchumananandasivam [58].

Fig. 4
figure 4

SEM micrograph of the sample at a 320x, b 500x, c 750x magnifications

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3.5 X-ray diffraction

In order to study the crystallinity of the material, it was characterized using XRD and mineral percentage as shown in Figs. 5 and 6 respectively. The sample shows three narrow peaks around 2θ = 34°, 45° and 65°, corresponding to the interplanary spacing of 1.38 Å, 1.09 Å and 0.85 Å, it is very intense, around 38°, which corresponds to the interplanary spacing of 1.25, showing the presence of crystalline regions in the sample. The major minerals present in the material include quartz (SiO2), marialite (Ca1.22 Na2.78) (Si9 Al3…), davyne (Na5.7 Ca0.5 (CO3)0.66(S…) and graphite (C), indicating the amorphous nature of the sample. However, a major diffraction was observed at 2θ = 38°. This result is confirmed by the XRF result. One of the major minerals present in the material is quartz, which is a chemical compound that consists of one atom of silicon and two atoms of oxygen, which makes the biochar a good semi-conductor source. The presence of graphite shows the biochar obtained is a major source of carbon which has diverse uses, including but not limited to adsorbent, conductive materials, etc. Moreover, the chicken feathers, although treated at a lower temperature in a heated retort reactor, displayed higher crystallinity when compared with others prepared with the conventional ones [9].

Fig. 5
figure 5

XRD Diffractogram of phases in the sample

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Fig. 6
figure 6

Pie-chart showing weight per fraction of the minerals in the sample

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3.6 X-ray fluorescence spectroscopy

Chicken feathers contain mainly keratin, which is an organic carbohydrate. It also contains some other elements that include potassium, manganese, iron, sulphur, calcium, nitrogen, phosphorus, chlorine and several other elements [59]. The feather type, species of bird, and type of food on which the bird feeds are major dependents of its constituents. Table 4 shows that CaO is the major metal oxide gotten from the conversion process, which is about 33.147 wt%. This was also gotten by Gusiatin, Kumpiene [21]. However P2O5 and SiO2 were also gotten as major oxides. These oxides are minor elements in this research, with their concentration being less than 10 wt%. SO3 is the second major oxide derived which could be from the raw components of the feather. Other oxides present are K2O, Cl, Fe2O3, and Al2O3. When chicken feather are being processed at increased temperature, the percentage of the mineral content is increased while that of the organic fraction reduced as they are removed from the process [21, 59, 60]. This justifies the reason for the high mineral content.

Table 4 Summary of the metal oxides present in the sample
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3.7 Energy dispersive spectroscopy

Table 5 displays the elemental composition of chicken feathers as determined by XRD-EDS. The major constituents are oxygen (36.917 wt%) and calcium (23.690 wt%), which are mainly from the raw feather, while sulphur, potassium, and chlorine content are 10.282 wt%, 8.154 wt%, and 7.258 wt%, respectively. The oxygen content gotten is increased compared to what was gotten in the raw chicken feathers as analyzed by Qu, Kang [46]. Other elemental constituents having less than 7 wt% are possibly present as oxides in the biochar. Its high content of calcium and oxygen shows its beneficial potential in water purification. Chen, Li [16] got a similar result in their work.

Table 5 Summary of the elemental composition of the sample
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4 Conclusion

Metal oxides were gotten from chicken feathers as analyzed in this work. The sample was found to be mesoporous in nature, which shows that it can be used in an adsorption process. The presence of the oxide and minerals was determined using XRF and XRD respectively and the result shows that the sample contains majorly CaO of 33.147 wt% while the minerals present are quartz, marialite, davyne, and graphite, indicating the amorphous nature of the sample. However, a major diffraction was observed at 2θ = 38° showing the presence of a crystalline property. A rougher structure was observed in the SEM micrographs, which could be as a result of the metallic oxide produced on the surface of the feather as the temperature is raised in the presence of a limited supply of oxygen. From the EDS analysis, oxygen and calcium are the major elements present in the material, albeit the sample also contains some other elements, including sulfur, potassium, and chlorine content. There was little disparity in the peaks observed when compared to that of raw chicken feathers from literature showing the effect of increased temperature on the sample. This study consequently opens up a novel energy-saving and sustainable approach for the preparation of metal oxides from poultry wastes and may be employed in other pyrolysis, adsorption, catalysis, and other product synthesis processes.