Testing leaching from sulfide-rich rock masses

In urban development projects, site preparation often requires excavation, resulting in the generation of rock masses. These masses are then reused to the greatest extent possible, although additional masses may also need to be purchased.

For land reclamation and to establish new marine habitats at Kolkajen in Stockholm Royal Seaport, rock masses will be reused. However, these rock masses may naturally contain sulfides, which could potentially impact the environment through leaching. This environmental impact occurs when sulfide minerals oxidize upon contact with air and water, leading to acidic leachate enriched with high concentrations of metals and sulfur being released into the recipient. Currently, risk assessments for sulfide-containing rock masses are primarily based on leaching characteristics under acidic conditions, such as those found in lakes. There is a knowledge gap regarding the risks and opportunities of using sulfide-rich rock for construction and structures in seawater. The risks of using such rock masses in a neutral environment like the Baltic Sea may be overestimated and need to be re-evaluated.

Objective and goals

The purpose of the research project "Recycling of Sulfide-Rich Construction Rock for Reef Building - Long-term Leaching Test in an Aquatic Environment" is to study the leaching of primarily iron sulfate in water and an oxygen-free environment. Should the study demonstrate minimal or no leaching, the rock masses could be reused.

The aim is to contribute new knowledge about the feasibility of using sulfide-bearing rocks for construction and infrastructure in water. Large reductions in transport to landfill sites would decrease both carbon emissions and costs related to transportation.

The tests will investigate the leaching of both unprocessed and processed rock material containing various levels of sulfide minerals in different types of aquatic environments such as lake water and salt water. Among other things, the tests will examine the chemical changes occurring in the surrounding water due to the rock's sulfide content and the environmental risks this poses. The testing locations are Loudden, part of the Stockholm Royal Seaport development project, and another site along Lake Mälaren.

During the study, a pool in Loudden will be filled with crushed rock into which water from the Baltic Sea will be pumped. Continuous measurements of pH, ionic strength, sulfide content, and elemental composition in the rock will then be taken. The study will also consider whether factors such as weather conditions might affect the results.

Results and Experiences

The investigations are ongoing and the final report will be presented in spring 2024.