Stung by a global pricing slump and liquidity issues, Grand Rapids-based Magnetation LLC said Tuesday that it has filed for Chapter 11 bankruptcy protection in an effort to restructure its debt and continue operating its iron ore concentration business. As part of the bankruptcy restructuring filed Monday, officials said they successfully reached an agreement with creditors of a note due in 2018 that will allow it to restructure its balance sheet and provide the cash needed to continue operations long term.