Abstract
With the increasing demands on more metals extraction, the hazardous waste resulted from mining industry has also raised. In this paper, the treatment process of nickel slag containing hazardous metals is described. The treatment involved a solidification process, where nickel slag is used as fine aggregates substituting agent. This study aimed to determine the optimum dosage of nickel slag that met specification in the construction of concrete floors. A series of technical feasibility test were carried out by replacing the weight proportions of sand with nickel slag gradually from 0% to 100% to examine the compressive strength, absorption rate, durability and leaching performance. The results indicated that even though all mixture variations possessed high value of absorption rate indicating high permeability concrete mix, all mixtures, however, had good durability. Furthermore, based on the compressive strength test, a mixture with 60% substitution of nickel slag is considered as a viable replacement of sand in the concrete floors construction in conformance to American Concrete Institute. The leaching performance test showed that leachability of heavy metals content, particularly Cr and Cd from mortar specimens were below the standard according to Indonesian Government Regulation No 101 of 2014, therefore, in terms of environmental point of view, the utilization of solidified nickel is considered safe to be used as concrete floors.
Highlights
Mining is one of the potential sectors that contribute to the national income, due to wide range of uses of metals and growing of their demand
The results show a decreasing trend as more nickel slag in the concrete mixtures. This is probably due to the high value of water to cement ratio in the mortar specimens with nickel slag
The high ratio of water to cement may be due to low water content in the nickel slag, which is 1.812%, that is quite lower than most aggregates value, which is lied between 3-8% [17]
Summary
Mining is one of the potential sectors that contribute to the national income, due to wide range of uses of metals and growing of their demand. The operation of mining industry could not be separated with the waste or by-products resulting from its process, of which hazardous waste is included. Rapid growth of mining industry has obviously led to steep increase of hazardous waste that should be properly managed. Slag is the most by-product left over in the mining industry, which resulted from a process separation between metals with its raw ore through heating process. The slag is produced in liquid form, but as the temperature cools down it is naturally transformed to be a solid. Slag can be found in the form of steel slags, phosphorus slag, zinc slag, nickel slag, etc, depending on the metals that the industry produces
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