Immobilization of Metals in Fired Clay Brick Incorporated with Aluminium-Rich Electroplating Sludge: Properties and Leaching Analysis

Abstract

Electroplating sludge is the hazardous waste discarded from the plating and extractive metallurgical process which can only be disposed of at a secured landfill. In this study, the physical and mechanical properties, as well as metal leaching analysis, of fired clay brick incorporated with electroplating sludge (0%, 2%, 4%, 6%, 8% and 10%) were determined. The physical and mechanical properties of bricks, such as firing shrinkage, dry density, initial rate of absorption, water absorption and compressive strength, were tested according to British standard 3921:1985 and British standard EN772:1. Furthermore, the metal leachability was determined by using the toxicity characteristic leaching procedure (TCLP) method 1311. The results show that the utilization of an electroplating-sludge brick up to 4% could enhance physical and mechanical properties, such as reducing the water absorption from 18.3% to 16.1% and increasing the compressive strength from 25.6 MPa to 41.6 MPa. The result also show that 4% of aluminium-rich electroplating sludge incorporated into the brick is the most suitable amount, as it leached less metal concentration and complied with USEPA standards. The metals which were most present in the electroplating sludge (aluminium and iron) drastically reduced from 193,000 ppm to 0.1372 ppm and from 4160 ppm to 0.144 ppm, respectively. Therefore, the electroplating sludge could be fully utilized in the fired clay brick as an alternative to producing low-cost building materials whilst decreasing the levels of disposal of metal sludge on the secured landfill.

1. Introduction

The rapid climb of industrialization in Malaysia has increased the demand for products and services, which has directly increased the waste generation of the country. For example, the electroplating industries generate a notable amount of electroplating waste, which is required to be treated before the disposal process. Based on the Malaysia Environmental Quality Report (MEQR) 2011 [1], heavy metal sludge was among the main wastes generated in Malaysia, accounting for 173,837.06 metric tons (MT) per annum, estimated as 10.72% of the total waste. There was a small rise in the volume of waste produced compared to 2010, where the general amount of heavy metal waste generated was 15,738,138 mt per annum. An outsized amount of sludge is produced by the physico-chemical treatment of the wastewater generated from the electroplating plant. The most common heavy metals which will be found in electroplating sludge include copper (Cu), lead (Pb), zinc (Zn), cadmium (Cd), chromium (Cr), iron (Fe) and manganese (Mn) [2].

The major environmental challenges in the electroplating industry come from the hazardous metals which must be properly treated and removed from wastewater. Some of the techniques used to eliminate heavy metal ions include chemical coagulation, ion exchange, oxidation, adsorption, membrane filtration and electrochemical treatment. However, most of these treatments have several disadvantages, such as insufficient removal capacity or the development of large quantities of sludge, and also require high capital running costs and technology [3]. Deposition into landfills is the most common method used to dispose of electroplating sludge. However, the disposal of electroplating sludge in landfill sites is not a particularly environmentally safe option. Several works, such as the use of an extraction solution with the help of extraction agents and the separation and recovery of the materials with ion exchange, extraction and adsorption, have been carried out to immobilize electroplating sludge with sorbents or cement, but the sorption or cementation techniques are not effective as solidifying/stabilizing technologies [4].

To address these problems, the search for better alternatives to replace the disposal method in metal waste management has been widely carried out. Many researchers are focusing on green technology as an alternative for the electroplating sludge disposal into the environment. Green technology is defined as the development and application of products, equipment and processes which have less impact on the environment. Moving towards sustainable building materials, the bricks or ceramics industries could be the best options to consume large amounts of electroplating sludge, as these materials are able to achieve the inertization and neutralization of electroplating sludge by encapsulating it in the matrix [5,6]. Many researchers have proven that the manufacturing of clay bricks plays a significant role in the greener management of hazardous wastes from different industrial processes [7,8,9].

Therefore, the purpose of this research is to explore the effectiveness of utilizing electroplating sludge to replace raw materials in the development of fired clay bricks and evaluate the performance of electroplating sludge bricks in terms of their physical and mechanical properties. Furthermore, the hazard of the leaching of metals from fired clay bricks is tested for environmental protection.

2. Materials and Methods

2.1. Raw Material Preparation

The raw materials for the brick samples, which were clay soil and electroplating sludge as shown in Figure 1, were collected from the Parit Sulong quarry and from aluminium electroplating industries located at Sri Gading and Batu Pahat, respectively. The raw materials were first dried in the oven for 24 h at 105 °C and left to be cooled to room temperature, before being ground and sieved to pass through a 5 mm sieve plate. The grinding process was carried out separately to prevent sample contamination. After grinding, both raw materials were kept in a closed cylindrical container before being used for brick manufacturing to avoid the entrance of unwanted substances and any reactivity of the raw materials with the external surroundings.

2.2. Geotechnical and Chemical Properties of the Raw Materials

The Atterberg limit test, which includes plastic limit and liquid limit, was carried out to evaluate the type and degree of plasticity of the soil which was being used throughout this study. Aside from that, the particle density test (conducted by using the pycnometer method based on BS 1377-2 [10]) was conducted to determine the specific gravities of the clay soil and electroplating sludge. The chemical properties of the raw materials were also analysed by using X-ray fluorescence (XRF) and the loss on ignition test. The loss on ignition value was obtained in accordance with BS 1377-3 [11] by igniting the raw materials at 750 °C in the furnace for a total duration of 4 h. In addition, the standard Proctor compaction test was also carried out to determine the optimum moisture needed for the control brick and the electroplating sludge bricks.

2.3. Manufacturing of Brick Samples

Six different percentages (0%, 2%, 4%, 6%, 8% and 10%) of electroplating sludge and clay soil were mixed with the optimum amount of water, as shown in

Table 1. Mixture design for electroplating sludge brick production.

Amount of Electroplating Sludge (%)	Amount of Clay Soil (kg)	Amount of Electroplating Sludge (kg)	Amount of Water (mL)
0	3.053	0.000	427.5
2	2.992	0.056	458.0
4	2.931	0.111	488.5
6	2.870	0.167	519.0
8	2.809	0.222	549.5
10	2.748	0.278	580.0

. The brick sample without the addition of electroplating sludge was labelled as the control brick (CB), whereas the brick samples with the addition of electroplating sludge were labelled as the electroplating sludge bricks (ESB). The control brick was manufactured as the reference to compare and evaluate the effects of electroplating sludge on the brick properties. The brick mixture was put in the mould (215 mm × 102.5 mm × 65 mm) of a semi-automated brick compression machine and compacted with a uniform pressure of 2000 psi.

Following this, the brick samples were dried in the oven for another 24 h to remove the moisture content before being fired in the furnace to the temperature of 1050 °C at a firing rate of 1 °C/min. Upon reaching the final temperature, the temperature was maintained for 2 h to ensure a uniform heat distribution to the bricks. Lastly, the bricks were left to undergo slow cooling in the furnace to allow the complete solidification of any liquids and the bonding of the brick mixture (Figure 2). This step was very crucial to avoid the cracking of the brick structure. Twenty brick samples with 6 different sludge percentages were manufactured to fulfil the requirements set by BS 3921:1985 [12].

2.4. Physical and Mechanical Testing of the Brick Samples

The physical and mechanical properties of the bricks that were tested in this study were firing shrinkage, dry density, initial rate of suction, water absorption and compressive strength. The procedures for testing were carried out following BS 3921:1985 [12]. The firing shrinkage was determined by measuring the length of the brick samples before and after firing. Meanwhile, the dry density was measured by the ratio of mass to volume. Furthermore, the initial rate of suction was investigated by obtaining the mass difference when soaking the surfaces of the brick samples within a water depth of 3 mm for 1 min, as depicted in Figure 3b. In contrast, the water absorption test was conducted by immersing the whole brick sample in the water bath for 5 h. For the compressive strength evaluation, the brick samples were compressed by using the compression testing machine Model NL 4000 X/006-A002 until reaching the maximum load of failure, as shown in Figure 3a. For each brick properties testing procedure, 10 out of 20 brick samples for each percentage were chosen randomly, and the property values were obtained from the average calculations.

2.5. Leachability Test of Metals

In this study, the possibility of metal leaching from the ESB samples was determined by using the toxicity characteristic leaching procedure (TCLP), following the guidelines of USEPA Method 1311 [13]. The extraction fluid for the TCLP was prepared by mixing 5.7 mL of glacial acetic acid with distilled water to the volume of 1 L. Then, the extraction of the TCLP sample for the metal analysis was carried out by placing the CB and ESB samples along with the extraction fluid into the 500 mL of high-density polyethylene (HDPE) bottle. The sample inside the HDPE bottle was then agitated by using an end-to-end rotary agitator for 18 ± 2 h at 30 rpm. After the agitation process, the sample was extracted and filtered through a 0.7 µm glass fibre filter using the vacuum filtration method, as exhibited in Figure 4. Lastly, the liquid sample was diluted to 10 and 100 times. and the metal analysis of the sample extraction was carried out by using inductively coupled plasma mass spectrometry (ICP-MS).

The metals that were analysed with ICP-MS were copper (Cu), lead (Pb), zinc (Zn), manganese (Mn), nickel (Ni), aluminium (Al), chromium (Cr), iron (Fe), cobalt (Co), arsenic (As) and cadmium (Cd). The analysed metals were recorded and compared against the concentration limits for metals set by the TCLP regulatory levels according to the United States Environmental Protection Agency [14].

3. Results and Discussion

3.1. Chemical Compositions of Raw Materials

The chemical compositions of the clay soil and electroplating sludge were analysed by using X-ray fluorescence (XRF) for elemental oxide.

Table 2. Chemical compositions of clay soil and electroplating sludge.

Chemical Elements	Concentration (%)
	Clay Soil	Electroplating Sludge
Sodium oxide	-	14.70
Magnesium oxide	1.87	-
Aluminium oxide	19.7	67.20
Silicon dioxide	67.6	3.02
Phosphorus (V) oxide	0.12	0.06
Sulphur trioxide	0.01	11.00
Potassium oxide	2.54	0.08
Calcium oxide	0.07	0.41
Strontium oxide	0.01	-
Iron (III) oxide	5.82	0.58
Titanium oxide	1.02	0.10
Copper (II) oxide	0.01	0.11
Chromium (III) oxide	0.01	0.02
Zinc oxide	0.01	0.03
Nickel oxide	-	0.05
Manganese (II) oxide	0.03	0.03
Cobalt oxide	0.03	0.01
Loss on Ignition	9.27	35.44

shows the concentrations of elemental oxide in the clay soil and electroplating sludge. From Table 2, it can be clearly seen that the major components of the clay soil are silicon dioxide (SiO₂) with 67.6 wt.%, followed by aluminium oxide (Al₂O₃) with 19.7 wt.% and (Fe₂O₃) with 5.82 wt.%. The three major components of clay soil are similar to both the typical clay soil used in the brick industry and to the findings obtained by Zhang et al. (2018) and L. Pérez-Villarejo et al. (2015) [15,16]. A high amount of SiO₂ present in the clay soil could provide the high strength to the bricks after the firing process. Additionally, the silicon dioxide content also promotes lower shrinkage during the drying and firing processes [17].

Furthermore, the percentage of the second-highest compound (Al₂O₃) present in the clay soil is optimum for the fired clay bricks for masonry walls application, as it is still within the range between 10 and 20 wt.%. Similarly, the iron oxide content in the clay soil is also favourable for brick manufacturing, as it does not exceed 10%. A higher amount of iron (III) oxide could lead to discoloration and efflorescence during the firing process, and would worsen the brick properties due to the black core formation if the brick were fired in a low oxygen atmosphere [17]. Contrary to this, aluminium oxide (Al₂O₃), sodium oxide (Na₂O) and sulphur trioxide (SO₃) are the predominant compounds present in the electroplating sludge, with 67.2 wt.%, 14.7 wt.% and 11 wt.%, respectively. It also contains a small amount of silicon dioxide (SiO₂) and a high-value of LOI. The high LOI value indicates that there is a high amount of mass loss for the electroplating sludge during the sludge brick firing, as it contains large amounts of hydroxides, organic matter and crystal water, which will dehydrate at temperatures above 900 °C [15]. Although a high LOI brings advantages such as producing lightweight bricks and providing energy for the firing process, it could also adversely impact the excessive increase in the porosity of the bricks [18]. The concentration of metal oxide in the electroplating sludge differs from that of Zhang et al. (2018) [15] and L. Pérez-Villarejo et al. (2015) [16], as the compositions are dependant on the nature of the chemical processes of the electroplating company.

Calcium oxide (CaO) was also present in the electroplating sludge at 0.41 wt.%. The presence of CaO in the sludge is due to the application of the heavy metals organic catcher in the flocculation and precipitation processes in the electroplating effluent treatment. Calcium compounds may exist in several forms, which are Ca(OH)₂, CaCO₃ and CaSO_4, which will decompose into CaO upon firing at a high temperature [19]. CaO has a huge influence on the heavy metal’s phase transformation and volatilization [20,21]. CaO might also trigger the oxidation of Cr(III) to Cr(IV) at a high temperature. Hence, low amounts of CaO are highly recommended to increase the stabilization efficiency of heavy metals [15]. It is also indicated that most metals in this sludge would not transform into an unstable state, which is favourable for reducing the toxic metal leaching.

3.2. Physical and Mechanical Properties of Bricks

3.2.1. Firing Shrinkage

The firing shrinkage of a brick is defined as its contraction due to the loss of capillary water [22]. When the water is evaporated into the environment, the clay particles will be closer together and result in the firing shrinkage. Figure 5 shows the results of firing shrinkage for the manufactured bricks. Based on Figure 5, the increasing trend of firing shrinkage with the addition of electroplating sludge can be observed. The ESB 10% possesses the highest value of firing shrinkage with the value of 3.53%. It was accompanied by the bricks with 8% and 6% of electroplating sludge, for which the values are 2.93% and 2.37%, respectively. Although the shrinkage value of the ESB is higher compared with the control brick, it still complies with the preferable shrinkage properties according to the standard, which is from 2.5% to 4% [12]. The shrinkage of electroplating sludge is higher compared to the control brick, which is probably due to the high loss on ignition value possessed by the electroplating sludge. The high LOI value indicates that the electroplating sludge consists of large amounts of hydroxides, organic matter and crystal water, which will dehydrate at temperatures above 900 °C and cause the increase in shrinkage.

3.2.2. Dry Density

The dry density was obtained based on the masses and volumes of the fired brick samples. From Figure 6, it can be observed that the dry density of the electroplating sludge bricks decreased with the increasing addition of electroplating sludge. There is no specific requirement in the British standard, Malaysian standard or ASTM international standard on the dry density. However, it can be observed that dry density decreases proportionally with the increment of electroplating sludge up to 8% and declines sharply when reaching 10%. During the firing process at elevated temperatures, the water is evaporated as steam, and organic substances are converted into combustible gases such as carbon dioxide and carbon monoxide [23,24].

The conversions of water and organic matter contribute to the weight loss of fired clay bricks. Furthermore, referring to the LOI value obtained, it is shown that the electroplating sludge used in this study comprises of high amounts of metal hydroxide and organic matter. These compounds will transform into gas components at the elevated temperatures. The density of the bricks gradually decreases due to the loss of the electroplating sludge components, which are incinerated at high temperatures during the firing process [16]. Moreover, the decrease in density with the addition of the 10% electroplating sludge is related to the specific gravity of the raw materials. The specific gravity of the electroplating sludge is 1.80 g/cm³, much lower than the specific gravity of the clay soil which is 2.53 g/cm³. In the ESB 10%, the amount of clay soil is much lower compared with different percentages, making the dry density of the ESB 10% much lower.

3.2.3. Initial Rate of Suction

The initial rate of suction measures the amount of water filtration on the brick’s surfaces. The initial rate of suction for all brick samples (except for the ESB 10%) comply with the typical IRS range for bricks, which is between 2% and 5% [25]. The value of the IRS should be lower than 5% to prevent the decrease of durability and provide greater resistance against the external environment. Based on Figure 7, the highest initial rate of suction (IRS) value recorded is 5.53 kg/m².min for 10% of electroplating sludge brick, followed by the 8% of electroplating sludge brick with an IRS value of 4.59 kg/m².min. The control brick reveals a significant difference in contrast with the electroplating sludge brick. The lowest IRS value obtained is 2.55 kg/m².min for the CB, followed by 2.81% and 3.70% for the ESB 2% and ESB 4%, respectively. The analysis shows that the IRS values increase as the percentages of electroplating sludge increase in the brick.

3.2.4. Water Absorption

Water absorption is a crucial index which needs to be studied for the evaluation of brick quality. It is highly related to the densification of the brick and the number of pores. In this study, the water absorption value was determined by referring to BS 3921:1985, in which the fired brick samples were immersed in the boiling water for 5 h. The increment weight was then measured to identify the value of water absorption. The water absorption values for the control brick and electroplating sludge bricks are illustrated in Figure 8.

The trend of the graph suggests that the water absorption of bricks with the addition of electroplating sludge up to 6% is lower than that of the control brick. The lowest water absorption percentage, which is 16.05%, was achieved by the ESB 4%, followed by the ESB 6% and ESB 2% with 17.25% and 17.42%, respectively. The ESB 8% and ESB 10% possess higher values of water absorption compared to the control brick (18.3%). The lowest water absorption value (observed for the ESB 4%) is similar to the outcomes of studies conducted by Dai et al. (2019) [23] and Pérez-Villarejo et al. (2015) [16]. Even though the water absorption value is high, all brick samples are still complying with the loading bearing and non-damp proof applications, since no limits are set in MS 1933-1 (except for damp-proof course brick). In addition, based on ASTM C62-127, ESB 4% complies with the requirement for the severe-weather-resistant-brick, with a water absorption value of less than 17%. Furthermore, other brick samples can be classified as moderate-weather-resistant-bricks with absorption values of less than 22%. The water absorption should be maintained at a range between 5% and 22% [25,26,27]. This is because a higher value would lead to cracks in the brick structure, whilst lower values would cause rainwater to run off quickly towards the mortar joints and enter the building, rather than be partially absorbed by the brick [26,27].

The water absorption of a brick is highly influenced by its pore volume and size. A smaller pore volume and size reduces the liquid absorption and decelerates the circulation of fluid within the brick material, leading to a lower rate of water absorption [28]. The reaction of compounds in fired clay bricks at high temperatures is also one of the contributing factors to the decline of water absorption. It was reported that silica and alumina reacted with Na₂O and K₂O at high temperatures and formed feldspar, which led to the improvement of water absorption [23]. As the electroplating sludge consists of high amounts of Na₂O (14.7%), there is a possibility that Na₂O reacts with the alumina and silica present in the clay soil and electroplating sludge. The different trends in water absorption and IRS is because in the IRS test, only one side of the brick surface is in contact with the water for 1 min. Meanwhile, in the water absorption test, the whole brick sample is fully immersed in a water bath for 5 h. The IRS test might demonstrate less accuracy compared with the water absorption test.

3.2.5. Compressive Strength

Compressive strength is the most important engineering property in brick production. The compressive strengths of the control brick and electroplating sludge bricks are summarized in Figure 9. As shown in the figure, the compressive strength of the fired clay bricks with the incorporation of electroplating sludge (up to 6%) is higher than the control brick. The electroplating sludge brick with 4% sludge has the highest compressive strength value at 41.53 MPa, followed by the ESB 6% and ESB 2% at 32.8 MPa and 32.3 MPa, respectively. Meanwhile, ESB 8% and ESB 10% possess the lowest values of compressive strength at 23.82 MPa and 17.98 MPa, respectively, which is much lower than the compressive strength of the control brick (25.56 MPa). The results suggest that the electroplating sludge percentage up to 6% could act as partial replacement material for clay soil for compressive strength enhancement, in which the maximum compressive strength was achieved when 4% of the electroplating sludge was used in the fired clay brick production.

Although it was observed that the compressive strength value for the ESB samples declined for ESB 8% and ESB 10%, all brick samples are still complying with the range set in BS 3921:1985 [12], which is between 7 MPa and 100 MPa, but the strength value is not sufficient for the bricks to be classified as engineering bricks based on BS EN 771-1 [29] and MS 1933-1 [30]. However, the CB, ESB 2%, ESB 4% and ESB 6% met the requirement as loading bearing four bricks. Meanwhile, the ESB 8% and ESB 10% can be classified as loading bearing three and loading bearing two, respectively, in MS 1933-1 [30]. Furthermore, ESB 4% can be classified as a severe-weather-resistant-brick according to ASTM C62-127 [31], as its compressive strength is higher than 20.7 MPa and the water absorption is lower than 17%. Other brick samples in this study also met the requirement as moderate-weather-resistant-bricks, with compressive strengths of more than 17.2 MPa and water absorption rates below 22%.

The increment of brick strength is possibly contributed to by the lower open porosity present in the ESB’s 2%, 4% and 6%, which is proven by the lower water absorption values and higher densities compared with the control brick, as reported in Figure 9. The formation of a glassy phase during the vitrification process at high temperatures closes the internal pore, resulting in brick densification [32]. Furthermore, the lower LOI value for the electroplating sludge used in this study indicates that the sludge contains a lower amount of organic matter and heavy metal hydroxide, thus decreasing the pore formation [5], which favoured the increase of compressive strength. Additionally, the decline of compressive strength for the 6%, 8% and 10% electroplating sludge additions is probably due to the irregular shapes formed by the reaction between the waste and clay soil composition [5].

3.3. Leachability of Metals

The toxicity characteristics leaching procedure (TCLP) was applied to simulate the leaching ability of the waste sample in the sanitary landfill if the waste was disposed of. The results in

Table 3. Leachability of metals of fired clay bricks incorporated with electroplating sludge and the metals regulation limit.

Metals	Concentration (ppm)
	CB	ESB2%	ESB4%	ESB6%	ESB8%	ESB10%	Raw Clay	Raw ES	TCLP	Permissible Limit for Drinking Water
									USEPA	USEPA 1996 [14]	WHO 2006 [37]	EPA 2001 [38]
Cu	0.0266	0.0461	0.0754	0.1300	0.0702	0.0634	94.00	1320.00	100	2	1	0.0266
Pb	0.0013	0.0016	0.0015	0.0048	0.0101 +++	0.0073 +++	16.60	91.00	5	0.01	0.005	0.0013
Zn	0.2160	0.2080	0.1080	0.1070	0.2750	0.1010	559.00	385.00	500	3	5	0.2160
Mn	0.0347	0.0282	0.0304	0.0380	0.3100 +++	0.3340 +++	1260.00	902.00	-	0.4	0.05	0.0347
Ni	0.0028	0.0108	0.0133	0.0219	0.0063	0.0030	59.90	308.00	1.34	0.07	0.1	0.0028
Al	0.0939	0.1372	0.1725	0.1814	4.3588 +++	6.5481 +++	3480.00	46,100.00	-	-	0.20	0.0939
Cr	0.0065	0.0024	0.0019	0.0023	0.0098	0.0040	7.97	171.00	5	0.05	-	0.0065
Fe	0.1440	0.2300	0.1450	0.2000	0.3610 +++	0.8730 +++	154.00	459.00	-	-	0.3	0.1440
Co	0.0003	0.0006	0.0000	0.0014	0.0002	0.0000	23.00	8.63	-	-	-	0.0003
As	0.0020	0.0023	0.0033	0.0073	0.0024	0.0003	0.55	19.70	5	0.01	0.01	0.0020

+++: not comply with EPA 2001.

show the metal leaching concentrations, as well as the metal leaching standards and the permissible limits for drinking water. It was observed that there are 11 metals leached from the electroplating-sludge brick, which are Cu, Pb, Zn, Mn, Ni, Al, Cr, Fe, Co, As and Cd. Aluminium (Al) possesses the highest metal element concentration leached from the electroplating sludge brick since the sludge was originated from the aluminium electroplating industry, followed by iron (Fe) and manganese (Mn). It was found that high amounts of metal were reduced significantly when comparing between the raw electroplating sludge and electroplating sludge brick. This proves that the metal elements in the electroplating sludge were encapsulated or transformed into more stable substances during the firing of the clay bricks at the elevated temperatures [33,34,35]. The presence of silica in the clay soil was also effective in enhancing the bonding between the raw material components and in enhancing the immobilization of the metals [36].

Furthermore, the leached concentrations of all metals were far below the metal leaching standard and permissible limits for drinking water, except for Al, Fe, Pb and Mn. The concentrations of these four metals exceeded the standard limit when the amount of electroplating sludge recycled was more than 8%. For instance, the Al present in the ESB 8% and ESB 10% electroplating-sludge brick was 10.358 ppm and 14.548 ppm, respectively, exceeding the standard limit. Meanwhile, the other metals such as Ni, Cr, Co, As and Cd possessed the lowest concentration values of the metals. The results indicate that 6% is the maximum electroplating sludge percentage that can be incorporated into the brick in order for it to comply with all three standards. However, it should be pointed out that the concentrations of metals in the leachate from the tests did not exceed the regulatory levels set out by the United States Environment Protection Agency [14].

4. Conclusions

In conclusion, the electroplating sludge has a good potential to act as a raw material in the fired clay brick production. The optimum percentage of electroplating sludge that could be incorporated into the fired clay brick is 4%, as it has the lowest water absorption rate (16.05%) and the highest compressive strength (41.53 MPa). Moreover, the leachate concentration of metals for the 4% electroplating sludge brick also complies with the USEPA standard and the permissible limit of drinking water. The physical and mechanical properties of all brick samples also comply with the brick standard. The outcomes of this study have deduced that the electroplating sludge utilization into fired clay bricks could be a viable option in producing an environmentally sustainable building material with adequate brick quality. Nevertheless, since the different sludge compositions and firing temperatures play a crucial role in the brick manufacturing, it is important to carry out a preliminary study to determine the optimum raw material composition and firing temperature for the enhancement of brick properties. It is also recommended to conduct an indoor air quality assessment to identify the potential airborne contaminants released from the exposed brick walls.